[svn-r22215] Description:

    Bring r22171 from trunk to 1.8 branch:

Bring "merge committed datatypes during H5Ocopy" feature from branch to
    trunk.  (Also has some minor bugfixes with it)

Tested on:
    Mac OSX/64 10.7.3 (amazon) w/debug
    (h5committest coming up)

26 files changed, 1397 insertions, 141 deletions

diff --git a/src/H5A.c b/src/H5A.c
index 8945669..221d190 100644
--- a/src/H5A.c
+++ b/src/H5A.c
@@ -2523,6 +2523,36 @@ done:
 
 
 /*-------------------------------------------------------------------------
+ * Function:    H5A_type
+ *
+ * Purpose:     Return the datatype for an attribute.
+ *
+ * Return:      Success:        Ptr to entry
+ *              Failure:        NULL
+ *
+ * Programmer:  Neil Fortner
+ *              Friday, November  11, 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+H5T_t *
+H5A_type(const H5A_t *attr)
+{
+    H5T_t *ret_value;   /* Return value */
+
+    FUNC_ENTER_NOAPI(NULL)
+
+    HDassert(attr);
+
+    /* Set return value */
+    ret_value = attr->shared->dt;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5A_type() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5Aexists
  *
  * Purpose:	Checks if an attribute with a given name exists on an opened
diff --git a/src/H5Apkg.h b/src/H5Apkg.h
index 20aa5b9..26c8dff 100644
--- a/src/H5Apkg.h
+++ b/src/H5Apkg.h
@@ -158,29 +158,6 @@ typedef struct {
     H5A_t       **attrs;        /* Pointer to array of attribute pointers */
 } H5A_attr_table_t;
 
-/* Attribute iteration operator for internal library callbacks */
-typedef herr_t (*H5A_lib_iterate_t)(const H5A_t *attr, void *op_data);
-
-/* Describe kind of callback to make for each attribute */
-typedef enum H5A_attr_iter_op_type_t {
-#ifndef H5_NO_DEPRECATED_SYMBOLS
-    H5A_ATTR_OP_APP,                /* Application callback */
-#endif /* H5_NO_DEPRECATED_SYMBOLS */
-    H5A_ATTR_OP_APP2,               /* Revised application callback */
-    H5A_ATTR_OP_LIB                 /* Library internal callback */
-} H5A_attr_iter_op_type_t;
-
-typedef struct H5A_attr_iter_op_t {
-    H5A_attr_iter_op_type_t op_type;
-    union {
-#ifndef H5_NO_DEPRECATED_SYMBOLS
-        H5A_operator1_t app_op;         /* Application callback for each attribute */
-#endif /* H5_NO_DEPRECATED_SYMBOLS */
-        H5A_operator2_t app_op2;        /* Revised application callback for each attribute */
-        H5A_lib_iterate_t lib_op;       /* Library internal callback for each attribute */
-    } u;
-} H5A_attr_iter_op_t;
-
 
 /*****************************/
 /* Package Private Variables */
@@ -268,9 +245,6 @@ H5_DLL herr_t H5O_attr_write(const H5O_loc_t *loc, hid_t dxpl_id,
     H5A_t *attr);
 H5_DLL herr_t H5O_attr_rename(const H5O_loc_t *loc, hid_t dxpl_id,
     const char *old_name, const char *new_name);
-H5_DLL herr_t H5O_attr_iterate(hid_t loc_id, hid_t dxpl_id, H5_index_t idx_type,
-    H5_iter_order_t order, hsize_t skip, hsize_t *last_attr,
-    const H5A_attr_iter_op_t *op, void *op_data);
 H5_DLL herr_t H5O_attr_remove(const H5O_loc_t *loc, const char *name,
     hid_t dxpl_id);
 H5_DLL herr_t H5O_attr_remove_by_idx(const H5O_loc_t *loc, H5_index_t idx_type,
diff --git a/src/H5Aprivate.h b/src/H5Aprivate.h
index 0c0e519..6646fa2 100644
--- a/src/H5Aprivate.h
+++ b/src/H5Aprivate.h
@@ -24,6 +24,8 @@
 
 /* Private headers needed by this file */
 #include "H5Gprivate.h"		/* Groups				*/
+#include "H5Oprivate.h"         /* Object headers                       */
+#include "H5Tprivate.h"         /* Datatypes                            */
 
 
 /**************************/
@@ -38,6 +40,29 @@
 /* Forward references of package typedefs */
 typedef struct H5A_t H5A_t;
 
+/* Attribute iteration operator for internal library callbacks */
+typedef herr_t (*H5A_lib_iterate_t)(const H5A_t *attr, void *op_data);
+
+/* Describe kind of callback to make for each attribute */
+typedef enum H5A_attr_iter_op_type_t {
+#ifndef H5_NO_DEPRECATED_SYMBOLS
+    H5A_ATTR_OP_APP,                /* Application callback */
+#endif /* H5_NO_DEPRECATED_SYMBOLS */
+    H5A_ATTR_OP_APP2,               /* Revised application callback */
+    H5A_ATTR_OP_LIB                 /* Library internal callback */
+} H5A_attr_iter_op_type_t;
+
+typedef struct H5A_attr_iter_op_t {
+    H5A_attr_iter_op_type_t op_type;
+    union {
+#ifndef H5_NO_DEPRECATED_SYMBOLS
+        H5A_operator1_t app_op;         /* Application callback for each attribute */
+#endif /* H5_NO_DEPRECATED_SYMBOLS */
+        H5A_operator2_t app_op2;        /* Revised application callback for each attribute */
+        H5A_lib_iterate_t lib_op;       /* Library internal callback for each attribute */
+    } u;
+} H5A_attr_iter_op_t;
+
 
 /*****************************/
 /* Library-private Variables */
@@ -51,6 +76,13 @@ typedef struct H5A_t H5A_t;
 /* General attribute routines */
 H5_DLL struct H5O_loc_t *H5A_oloc(H5A_t *attr);
 H5_DLL H5G_name_t *H5A_nameof(H5A_t *attr);
+H5_DLL H5T_t *H5A_type(const H5A_t *attr);
+H5_DLL herr_t H5O_attr_iterate_real(hid_t loc_id, const H5O_loc_t *loc,
+    hid_t dxpl_id, H5_index_t idx_type, H5_iter_order_t order, hsize_t skip,
+    hsize_t *last_attr, const H5A_attr_iter_op_t *attr_op, void *op_data);
+H5_DLL herr_t H5O_attr_iterate(hid_t loc_id, hid_t dxpl_id, H5_index_t idx_type,
+    H5_iter_order_t order, hsize_t skip, hsize_t *last_attr,
+    const H5A_attr_iter_op_t *op, void *op_data);
 
 #endif /* _H5Aprivate_H */
 
diff --git a/src/H5Oainfo.c b/src/H5Oainfo.c
index 78b17e0..8a146c4 100644
--- a/src/H5Oainfo.c
+++ b/src/H5Oainfo.c
@@ -46,11 +46,11 @@ static herr_t H5O_ainfo_delete(H5F_t *f, hid_t dxpl_id, H5O_t *open_oh,
 static herr_t H5O_ainfo_pre_copy_file(H5F_t *file_src, const void *mesg_src,
     hbool_t *deleted, const H5O_copy_t *cpy_info, void *udata);
 static void *H5O_ainfo_copy_file(H5F_t *file_src, void *mesg_src,
-    H5F_t *file_dst, hbool_t *recompute_size, H5O_copy_t *cpy_info, void *udata,
-    hid_t dxpl_id);
+    H5F_t *file_dst, hbool_t *recompute_size, unsigned *mesg_flags,
+    H5O_copy_t *cpy_info, void *udata, hid_t dxpl_id);
 static herr_t H5O_ainfo_post_copy_file(const H5O_loc_t *src_oloc,
-    const void *mesg_src, H5O_loc_t *dst_oloc, void *mesg_dst, hid_t dxpl_id,
-    H5O_copy_t *cpy_info);
+    const void *mesg_src, H5O_loc_t *dst_oloc, void *mesg_dst,
+    unsigned *mesg_flags, hid_t dxpl_id, H5O_copy_t *cpy_info);
 static herr_t H5O_ainfo_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg,
 			     FILE * stream, int indent, int fwidth);
 
@@ -403,7 +403,8 @@ H5O_ainfo_pre_copy_file(H5F_t UNUSED *file_src, const void UNUSED *native_src,
  */
 static void *
 H5O_ainfo_copy_file(H5F_t *file_src, void *mesg_src, H5F_t *file_dst,
-    hbool_t UNUSED *recompute_size, H5O_copy_t *cpy_info, void UNUSED *udata, hid_t dxpl_id)
+    hbool_t UNUSED *recompute_size, unsigned UNUSED *mesg_flags,
+    H5O_copy_t *cpy_info, void UNUSED *udata, hid_t dxpl_id)
 {
     H5O_ainfo_t *ainfo_src = (H5O_ainfo_t *)mesg_src;
     H5O_ainfo_t *ainfo_dst = NULL;
@@ -462,7 +463,8 @@ done:
  */
 static herr_t
 H5O_ainfo_post_copy_file(const H5O_loc_t *src_oloc, const void *mesg_src,
-    H5O_loc_t *dst_oloc, void *mesg_dst, hid_t dxpl_id, H5O_copy_t *cpy_info)
+    H5O_loc_t *dst_oloc, void *mesg_dst, unsigned UNUSED *mesg_flags,
+    hid_t dxpl_id, H5O_copy_t *cpy_info)
 {
     const H5O_ainfo_t *ainfo_src = (const H5O_ainfo_t *)mesg_src;
     herr_t ret_value = SUCCEED;   /* Return value */
diff --git a/src/H5Oattr.c b/src/H5Oattr.c
index 8cd243b..510d64f 100644
--- a/src/H5Oattr.c
+++ b/src/H5Oattr.c
@@ -61,6 +61,7 @@ static herr_t H5O_attr_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg,
 #define H5O_SHARED_COPY_FILE_REAL	H5O_attr_copy_file
 #define H5O_SHARED_POST_COPY_FILE	H5O_attr_shared_post_copy_file
 #define H5O_SHARED_POST_COPY_FILE_REAL	H5O_attr_post_copy_file
+#undef  H5O_SHARED_POST_COPY_FILE_UPD
 #define H5O_SHARED_DEBUG		H5O_attr_shared_debug
 #define H5O_SHARED_DEBUG_REAL		H5O_attr_debug
 #include "H5Oshared.h"			/* Shared Object Header Message Callbacks */
diff --git a/src/H5Oattribute.c b/src/H5Oattribute.c
index e36d4ab..bbaf72b 100644
--- a/src/H5Oattribute.c
+++ b/src/H5Oattribute.c
@@ -135,9 +135,6 @@ typedef struct {
 /********************/
 /* Local Prototypes */
 /********************/
-static herr_t H5O_attr_iterate_real(hid_t loc_id, const H5O_loc_t *loc,
-    hid_t dxpl_id, H5_index_t idx_type, H5_iter_order_t order, hsize_t skip,
-    hsize_t *last_attr, const H5A_attr_iter_op_t *attr_op, void *op_data);
 static htri_t H5O_attr_find_opened_attr(const H5O_loc_t *loc, H5A_t **attr,
     const char* name_to_open);
 
@@ -1283,7 +1280,7 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-static herr_t
+herr_t
 H5O_attr_iterate_real(hid_t loc_id, const H5O_loc_t *loc, hid_t dxpl_id,
     H5_index_t idx_type, H5_iter_order_t order, hsize_t skip,
     hsize_t *last_attr, const H5A_attr_iter_op_t *attr_op, void *op_data)
diff --git a/src/H5Ocopy.c b/src/H5Ocopy.c
index d9a4b42..95a2e75 100644
--- a/src/H5Ocopy.c
+++ b/src/H5Ocopy.c
@@ -34,6 +34,7 @@
 /* Headers */
 /***********/
 #include "H5private.h"		/* Generic Functions			*/
+#include "H5Aprivate.h"         /* Attributes                           */
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5FLprivate.h"	/* Free lists                           */
 #include "H5Iprivate.h"		/* IDs			  		*/
@@ -54,6 +55,20 @@
 /* Local Typedefs */
 /******************/
 
+/* Key object for skiplist of committed datatypes */
+typedef struct H5O_copy_search_comm_dt_key_t {
+    H5T_t               *dt;    /* Datatype */
+    unsigned long       fileno; /* File number */
+} H5O_copy_search_comm_dt_key_t;
+
+/* Callback struct for building a list of committed datatypes */
+typedef struct H5O_copy_search_comm_dt_ud_t {
+    H5SL_t      *dst_dt_list;   /* Skip list of committed datatypes */
+    H5G_loc_t   *dst_root_loc;  /* Starting location for iteration */
+    H5O_loc_t   obj_oloc;       /* Object location (for attribute iteration callback) */
+    hid_t       dxpl_id;        /* Dataset transfer property list id */
+} H5O_copy_search_comm_dt_ud_t;
+
 
 /********************/
 /* Package Typedefs */
@@ -65,14 +80,23 @@
 /********************/
 
 static herr_t H5O_copy_free_addrmap_cb(void *item, void *key, void *op_data);
-static herr_t H5O_copy_header_real(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
+static herr_t H5O_copy_header_real(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out*/,
     hid_t dxpl_id, H5O_copy_t *cpy_info, H5O_type_t *obj_type, void **udata);
-static herr_t H5O_copy_header(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
-    hid_t dxpl_id, unsigned cpy_option);
+static herr_t H5O_copy_header(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out*/,
+    hid_t dxpl_id, hid_t ocpypl_id);
 static herr_t H5O_copy_obj(H5G_loc_t *src_loc, H5G_loc_t *dst_loc,
     const char *dst_name, hid_t ocpypl_id, hid_t lcpl_id);
 static herr_t H5O_copy_obj_by_ref(H5O_loc_t *src_oloc, hid_t dxpl_id,
     H5O_loc_t *dst_oloc, H5G_loc_t *dst_root_loc, H5O_copy_t *cpy_info);
+static herr_t H5O_copy_free_comm_dt_cb(void *item, void *key, void *op_data);
+static int H5O_copy_comm_dt_cmp(const void *dt1, const void *dt2);
+static herr_t H5O_copy_search_comm_dt_cb(hid_t group, const char *name,
+    const H5L_info_t *linfo, void *udata);
+static htri_t H5O_copy_search_comm_dt(H5F_t *file_src, H5O_t *oh_src,
+    H5O_loc_t *oloc_dst/*in, out*/, hid_t dxpl_id, H5O_copy_t *cpy_info);
+static herr_t H5O_copy_insert_comm_dt(H5F_t *file_src, H5O_t *oh_src,
+    H5O_loc_t *oloc_dst, hid_t dxpl_id, H5O_copy_t *cpy_info);
+
 
 /*********************/
 /* Package Variables */
@@ -81,6 +105,12 @@ static herr_t H5O_copy_obj_by_ref(H5O_loc_t *src_oloc, hid_t dxpl_id,
 /* Declare a free list to manage the H5O_addr_map_t struct */
 H5FL_DEFINE(H5O_addr_map_t);
 
+/* Declare a free list to manage the H5O_copy_search_comm_dt_key_t struct */
+H5FL_DEFINE(H5O_copy_search_comm_dt_key_t);
+
+/* Declare a free list to manage haddr_t variables */
+H5FL_DEFINE(haddr_t);
+
 
 /*****************************/
 /* Library Private Variables */
@@ -284,8 +314,9 @@ done:
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5O_copy_header_real(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
-    hid_t dxpl_id, H5O_copy_t *cpy_info, H5O_type_t *obj_type, void **udata)
+H5O_copy_header_real(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out*/,
+    hid_t dxpl_id, H5O_copy_t *cpy_info, H5O_type_t *obj_type,
+    void **udata /*out*/)
 {
     H5O_addr_map_t         *addr_map = NULL;       /* Address mapping of object copied */
     H5O_t                  *oh_src = NULL;         /* Object header for source object */
@@ -329,6 +360,53 @@ H5O_copy_header_real(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
             (NULL == (cpy_udata = (obj_class->get_copy_file_udata)())))
         HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to retrieve copy user data")
 
+    /* If we are merging committed datatypes, check for a match in the destination
+     * file now */
+    if(cpy_info->merge_comm_dt && obj_class->type == H5O_TYPE_NAMED_DATATYPE) {
+        unsigned long fileno_src; /* fileno for source file */
+        unsigned long fileno_dst; /* fileno for destination file */
+        htri_t merge; /* Whether we found a match in the destination file */
+
+        /* Check if the source and dest file are the same.  If so, just return
+         * the source object address */
+        H5F_GET_FILENO(oloc_src->file, fileno_src);
+        H5F_GET_FILENO(oloc_dst->file, fileno_dst);
+        if(fileno_src == fileno_dst) {
+            merge = TRUE;
+            oloc_dst->addr = oloc_src->addr;
+        } /* end if */
+        else
+            /* Search for a matching committed datatype, building the list if
+             * necessary */
+            if((merge = H5O_copy_search_comm_dt(oloc_src->file, oh_src, oloc_dst, dxpl_id, cpy_info)) < 0)
+                HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't search for matching committed datatype")
+
+        if(merge) {
+            /* Found a match, add to skip list and exit */
+            /* Allocate space for the address mapping of the object copied */
+            if(NULL == (addr_map = H5FL_MALLOC(H5O_addr_map_t)))
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+            /* Insert the address mapping for the found object into the copied
+             * list */
+            addr_map->src_obj_pos.fileno = fileno_src;
+            addr_map->src_obj_pos.addr = oloc_src->addr;
+            addr_map->dst_addr = oloc_dst->addr;
+            addr_map->is_locked = TRUE;                 /* We've locked the object currently */
+            addr_map->inc_ref_count = 0;                /* Start with no additional ref counts to add */
+            addr_map->obj_class = obj_class;
+            addr_map->udata = cpy_udata;
+
+            /* Insert into skip list */
+            if(H5SL_insert(cpy_info->map_list, addr_map, &(addr_map->src_obj_pos)) < 0) {
+                addr_map = H5FL_FREE(H5O_addr_map_t, addr_map);
+                HGOTO_ERROR(H5E_OHDR, H5E_CANTINSERT, FAIL, "can't insert object into skip list")
+            } /* end if */
+
+            HGOTO_DONE(SUCCEED)
+        } /* end if */
+    } /* end if */
+
     /* Flush any dirty messages in source object header to update the header chunks */
     if(H5O_flush_msgs(oloc_src->file, oh_src) < 0)
         HGOTO_ERROR(H5E_OHDR, H5E_CANTFLUSH, FAIL, "unable to flush object header messages")
@@ -470,38 +548,33 @@ H5O_copy_header_real(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
 
         /* copy this message into destination file */
         if(copy_type->copy_file) {
-            htri_t is_shared;           /* Whether message is shared */
             hbool_t recompute_size;     /* Whether copy_file callback created a shared message */
+            unsigned mesg_flags;        /* Message flags */
 
             /* Decode the message if necessary. */
             H5O_LOAD_NATIVE(oloc_src->file, dxpl_id, 0, oh_src, mesg_src, FAIL)
 
+            /* Get destination message flags, and unset shared and shareable
+             * flags.  mesg_dst->flags will contain the original flags for now.
+             */
+            mesg_flags = (unsigned)mesg_dst->flags & ~H5O_MSG_FLAG_SHARED
+                    & ~H5O_MSG_FLAG_SHAREABLE;
+
             /* Copy the source message */
             recompute_size = FALSE;
-            if((mesg_dst->native = H5O_msg_copy_file(copy_type,
-                    oloc_src->file, mesg_src->native, oloc_dst->file,
-                    &recompute_size, cpy_info, cpy_udata, dxpl_id)) == NULL)
+            if((mesg_dst->native = H5O_msg_copy_file(copy_type, oloc_src->file,
+                    mesg_src->native, oloc_dst->file, &recompute_size,
+                    &mesg_flags, cpy_info, cpy_udata, dxpl_id)) == NULL)
                 HGOTO_ERROR(H5E_OHDR, H5E_CANTCOPY, FAIL, "unable to copy object header message")
 
-            /* Check if new message is shared */
-            if((is_shared = H5O_msg_is_shared(copy_type->id, mesg_dst->native)) < 0)
-                HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "unable to query message's shared status")
-
-            /* In being copied, the message may have become shared or stopped
-             * being shared, set/unset its sharing flag.
+            /* Check if the sharing state changed, and recompute the size if so
              */
-            if(is_shared && !(mesg_dst->flags & H5O_MSG_FLAG_SHARED)) {
-                mesg_dst->flags |= H5O_MSG_FLAG_SHARED;
-
-                /* Recompute message size (mesg_dst->native is really shared) */
-                 recompute_size = TRUE;
-            } /* end if */
-            else if(!is_shared && (mesg_dst->flags & H5O_MSG_FLAG_SHARED)) {
-                mesg_dst->flags &= ~H5O_MSG_FLAG_SHARED;
-
-                /* Recompute message size (msg_dest->native is no longer shared) */
+            if(!(mesg_flags & H5O_MSG_FLAG_SHARED)
+                    != !(mesg_dst->flags & H5O_MSG_FLAG_SHARED))
                 recompute_size = TRUE;
-            } /* end if */
+
+            /* Set destination message flags */
+            mesg_dst->flags = (uint8_t)mesg_flags;
 
             /* Recompute message's size */
             /* (its sharing status or one of its components (for attributes)
@@ -671,6 +744,13 @@ H5O_copy_header_real(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
     oloc_dst->addr = addr_new;
 
 
+    /* If we are merging committed datatypes and this is a committed datatype, insert
+     * the copied datatype into the list of committed datatypes in the target file.
+     */
+    if(cpy_info->merge_comm_dt && obj_class->type == H5O_TYPE_NAMED_DATATYPE)
+        if(H5O_copy_insert_comm_dt(oloc_src->file, oh_src, oloc_dst, dxpl_id, cpy_info) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't insert committed datatype into destination list")
+
     /* Allocate space for the address mapping of the object copied */
     if(NULL == (addr_map = H5FL_MALLOC(H5O_addr_map_t)))
         HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
@@ -686,8 +766,10 @@ H5O_copy_header_real(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
     addr_map->udata = cpy_udata;
 
     /* Insert into skip list */
-    if(H5SL_insert(cpy_info->map_list, addr_map, &(addr_map->src_obj_pos)) < 0)
+    if(H5SL_insert(cpy_info->map_list, addr_map, &(addr_map->src_obj_pos)) < 0) {
+        addr_map = H5FL_FREE(H5O_addr_map_t, addr_map);
         HGOTO_ERROR(H5E_OHDR, H5E_CANTINSERT, FAIL, "can't insert object into skip list")
+    } /* end if */
 
     /* "post copy" loop over messages, to fix up any messages which require a complete
      * object header for destination object
@@ -716,17 +798,26 @@ H5O_copy_header_real(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
         HDassert(copy_type);
 
         if(copy_type->post_copy_file && mesg_src->native) {
+            unsigned mesg_flags;        /* Message flags */
+
             /* Sanity check destination message */
             HDassert(mesg_dst->type == mesg_src->type);
             HDassert(mesg_dst->native);
 
+            /* Get destination message flags.   mesg_dst->flags will contain the
+             * original flags for now. */
+            mesg_flags = (unsigned)mesg_dst->flags;
+
             /* the object header is needed in the post copy for shared message */
             cpy_info->oh_dst = oh_dst;
 
             /* Perform "post copy" operation on message */
             if((copy_type->post_copy_file)(oloc_src, mesg_src->native, oloc_dst,
-                    mesg_dst->native, dxpl_id, cpy_info) < 0)
+                    mesg_dst->native, &mesg_flags, dxpl_id, cpy_info) < 0)
                 HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to perform 'post copy' operation on message")
+
+            /* Verify that the flags did not change */
+            HDassert(mesg_flags == (unsigned) mesg_dst->flags);
         } /* end if */
     } /* end for */
 
@@ -787,9 +878,9 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5O_copy_header_map(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
+H5O_copy_header_map(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out*/,
     hid_t dxpl_id, H5O_copy_t *cpy_info, hbool_t inc_depth,
-    H5O_type_t *obj_type, void **udata)
+    H5O_type_t *obj_type, void **udata /*out*/)
 {
     H5O_addr_map_t      *addr_map = NULL;       /* Address mapping of object copied */
     H5_obj_t            src_obj_pos;            /* Position of source object */
@@ -927,9 +1018,13 @@ H5O_copy_free_addrmap_cb(void *_item, void UNUSED *key, void UNUSED *op_data)
  */
 static herr_t
 H5O_copy_header(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
-    hid_t dxpl_id, unsigned cpy_option)
+    hid_t dxpl_id, hid_t ocpypl_id)
 {
     H5O_copy_t  cpy_info;               /* Information for copying object */
+    H5P_genplist_t  *ocpy_plist;        /* Object copy property list created */
+    H5O_copy_dtype_merge_list_t *dt_list = NULL; /* List of datatype merge suggestions */
+    H5O_mcdt_cb_info_t   cb_info;      	/* Callback info struct */
+    unsigned    cpy_option = 0;         /* Copy options */
     herr_t      ret_value = SUCCEED;
 
     FUNC_ENTER_NOAPI_NOINIT
@@ -939,6 +1034,22 @@ H5O_copy_header(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
     HDassert(H5F_addr_defined(oloc_src->addr));
     HDassert(oloc_dst->file);
 
+    /* Get the copy property list */
+    if(NULL == (ocpy_plist = (H5P_genplist_t *)H5I_object(ocpypl_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a property list")
+
+    /* Retrieve the copy parameters */
+    if(H5P_get(ocpy_plist, H5O_CPY_OPTION_NAME, &cpy_option) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get object copy flag")
+
+    /* Retrieve the marge committed datatype list */
+    if(H5P_get(ocpy_plist, H5O_CPY_MERGE_COMM_DT_LIST_NAME, &dt_list) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get merge committed datatype list")
+
+    /* Get callback info */
+    if(H5P_get(ocpy_plist, H5O_CPY_MCDT_SEARCH_CB_NAME, &cb_info) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get callback info")
+
     /* Convert copy flags into copy struct */
     HDmemset(&cpy_info, 0, sizeof(H5O_copy_t));
     if((cpy_option & H5O_COPY_SHALLOW_HIERARCHY_FLAG) > 0) {
@@ -958,9 +1069,18 @@ H5O_copy_header(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
         cpy_info.copy_without_attr = TRUE;
     if((cpy_option & H5O_COPY_PRESERVE_NULL_FLAG) > 0)
         cpy_info.preserve_null = TRUE;
+    if((cpy_option & H5O_COPY_MERGE_COMMITTED_DTYPE_FLAG) > 0)
+        cpy_info.merge_comm_dt = TRUE;
+
+    /* Add dt_list to copy struct */
+    cpy_info.dst_dt_suggestion_list = dt_list;
+
+    /* Add set callback information */
+    cpy_info.mcdt_cb = cb_info.func;
+    cpy_info.mcdt_ud = cb_info.user_data;
 
     /* Create a skip list to keep track of which objects are copied */
-    if((cpy_info.map_list = H5SL_create(H5SL_TYPE_OBJ, NULL)) == NULL)
+    if(NULL == (cpy_info.map_list = H5SL_create(H5SL_TYPE_OBJ, NULL)))
         HGOTO_ERROR(H5E_SLIST, H5E_CANTCREATE, FAIL, "cannot make skip list")
 
     /* copy the object from the source file to the destination file */
@@ -970,6 +1090,8 @@ H5O_copy_header(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
 done:
     if(cpy_info.map_list)
         H5SL_destroy(cpy_info.map_list, H5O_copy_free_addrmap_cb, NULL);
+    if(cpy_info.dst_dt_list)
+        H5SL_destroy(cpy_info.dst_dt_list, H5O_copy_free_comm_dt_cb, NULL);
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5O_copy_header() */
@@ -991,14 +1113,12 @@ static herr_t
 H5O_copy_obj(H5G_loc_t *src_loc, H5G_loc_t *dst_loc, const char *dst_name,
     hid_t ocpypl_id, hid_t lcpl_id)
 {
-    H5P_genplist_t  *ocpy_plist=NULL;           /* Object copy property list created */
-    hid_t           dxpl_id=H5AC_dxpl_id;
     H5G_name_t      new_path;                   /* Copied object group hier. path */
     H5O_loc_t       new_oloc;                   /* Copied object object location */
     H5G_loc_t       new_loc;                    /* Group location of object copied */
     H5F_t           *cached_dst_file;           /* Cached destination file */
-    hbool_t         entry_inserted=FALSE;       /* Flag to indicate that the new entry was inserted into a group */
-    unsigned        cpy_option = 0;             /* Copy options */
+    hbool_t         entry_inserted = FALSE;     /* Flag to indicate that the new entry was inserted into a group */
+    hid_t           dxpl_id = H5AC_dxpl_id;     /* DXPL for operation */
     herr_t          ret_value = SUCCEED;        /* Return value */
 
     FUNC_ENTER_NOAPI(FAIL)
@@ -1009,14 +1129,6 @@ H5O_copy_obj(H5G_loc_t *src_loc, H5G_loc_t *dst_loc, const char *dst_name,
     HDassert(dst_loc->oloc->file);
     HDassert(dst_name);
 
-    /* Get the copy property list */
-    if(NULL == (ocpy_plist = (H5P_genplist_t *)H5I_object(ocpypl_id)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a property list")
-
-    /* Retrieve the copy parameters */
-    if(H5P_get(ocpy_plist, H5O_CPY_OPTION_NAME, &cpy_option) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get object copy flag")
-
     /* Set up copied object location to fill in */
     new_loc.oloc = &new_oloc;
     new_loc.path = &new_path;
@@ -1029,7 +1141,7 @@ H5O_copy_obj(H5G_loc_t *src_loc, H5G_loc_t *dst_loc, const char *dst_name,
     cached_dst_file = dst_loc->oloc->file;
 
     /* Copy the object from the source file to the destination file */
-    if(H5O_copy_header(src_loc->oloc, &new_oloc, dxpl_id, cpy_option) < 0)
+    if(H5O_copy_header(src_loc->oloc, &new_oloc, dxpl_id, ocpypl_id) < 0)
         HGOTO_ERROR(H5E_OHDR, H5E_CANTCOPY, FAIL, "unable to copy object")
 
     /* Patch dst_loc.  Again, this can be removed once oloc's point to shared
@@ -1245,3 +1357,579 @@ done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5O_copy_expand_ref() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_copy_free_comm_dt_cb
+ *
+ * Purpose:     Frees the merge committed dt skip list key and object.
+ *
+ * Return:      SUCCEED (never fails)
+ *
+ * Programmer:  Neil Fortner
+ *              Oct 6 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_copy_free_comm_dt_cb(void *item, void *_key, void UNUSED *op_data)
+{
+    haddr_t     *addr = (haddr_t *)item;
+    H5O_copy_search_comm_dt_key_t *key = (H5O_copy_search_comm_dt_key_t *)_key;
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    HDassert(addr);
+    HDassert(key);
+    HDassert(key->dt);
+
+    key->dt = (H5T_t *)H5O_msg_free(H5O_DTYPE_ID, key->dt);
+    key = H5FL_FREE(H5O_copy_search_comm_dt_key_t, key);
+    addr = H5FL_FREE(haddr_t, addr);
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5O_copy_free_comm_dt_cb */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_copy_comm_dt_cmp
+ *
+ * Purpose:     Skiplist callback used to compare 2 keys for the merge
+ *              committed dt list.  Mostly a wrapper for H5T_cmp.
+ *
+ * Return:      0 if key1 and key2 are equal.
+ *              <0 if key1 is less than key2.
+ *              >0 if key1 is greater than key2.
+ *
+ * Programmer:  Neil Fortner
+ *              Oct 6 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+H5O_copy_comm_dt_cmp(const void *_key1, const void *_key2)
+{
+    const H5O_copy_search_comm_dt_key_t *key1 = (const H5O_copy_search_comm_dt_key_t *)_key1;
+    const H5O_copy_search_comm_dt_key_t *key2 = (const H5O_copy_search_comm_dt_key_t *)_key2;
+    int ret_value = 0;
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    /* Check fileno.  It is unlikely to be different so check if they are equal
+     * first so only one comparison needs to be made. */
+    if(key1->fileno != key2->fileno) {
+        if(key1->fileno < key2->fileno)
+            HGOTO_DONE(-1)
+        if(key1->fileno > key2->fileno)
+            HGOTO_DONE(1)
+    } /* end if */
+
+    ret_value = H5T_cmp(key1->dt, key2->dt, FALSE);
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_copy_comm_dt_cmp */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_copy_search_comm_dt_attr_cb
+ *
+ * Purpose:     Callback for H5O_attr_iterate_real from
+ *              H5O_copy_search_comm_dt_check.  Checks if the attribute's
+ *              datatype is committed.  If it is, adds it to the merge
+ *              committed dt skiplist present in udata if it does not match
+ *              any already present.
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Nov 3 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_copy_search_comm_dt_attr_cb(const H5A_t *attr, void *_udata)
+{
+    H5O_copy_search_comm_dt_ud_t *udata = (H5O_copy_search_comm_dt_ud_t *)_udata;
+    H5T_t       *dt = NULL;             /* Datatype */
+    H5O_copy_search_comm_dt_key_t *key = NULL; /* Skiplist key */
+    haddr_t     *addr = NULL;           /* Destination address */
+    hbool_t     obj_inserted = FALSE;   /* Object inserted into skip list */
+    herr_t      ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    /* Sanity checks */
+    HDassert(attr);
+    HDassert(udata);
+    HDassert(udata->dst_dt_list);
+    HDassert(H5F_addr_defined(udata->obj_oloc.addr));
+
+    /* Get attribute datatype */
+    if(NULL == (dt = H5A_type(attr)))
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't get attribute datatype")
+
+    /* Check if the datatype is committed and search the skip list if so */
+    if(H5T_committed(dt)) {
+        /* Allocate key */
+        if(NULL == (key = H5FL_MALLOC(H5O_copy_search_comm_dt_key_t)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+        /* Copy datatype into key */
+        if(NULL == (key->dt = (H5T_t *)H5O_msg_copy(H5O_DTYPE_ID, dt, NULL)))
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to copy datatype message")
+
+        /* Get datatype object fileno */
+        H5F_GET_FILENO(udata->obj_oloc.file, key->fileno);
+
+        if(!H5SL_search(udata->dst_dt_list, key)) {
+            /* Allocate destination address */
+            if(NULL == (addr = H5FL_MALLOC(haddr_t)))
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+            /* Add the destination datatype to the skip list */
+            *addr = ((H5O_shared_t *)(key->dt))->u.loc.oh_addr;
+            if(H5SL_insert(udata->dst_dt_list, addr, key) < 0)
+                HGOTO_ERROR(H5E_OHDR, H5E_CANTINSERT, FAIL, "can't insert object into skip list")
+            obj_inserted = TRUE;
+        } /* end if */
+    } /* end if */
+
+done:
+    /* Release resources */
+    if(!obj_inserted) {
+        if(key) {
+            if(key->dt)
+                key->dt = (H5T_t *)H5O_msg_free(H5O_DTYPE_ID, key->dt);
+            key = H5FL_FREE(H5O_copy_search_comm_dt_key_t, key);
+        } /* end if */
+        if(addr) {
+            HDassert(ret_value < 0);
+            addr = H5FL_FREE(haddr_t, addr);
+        } /* end if */
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_copy_search_comm_dt_attr_cb */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_copy_search_comm_dt_check
+ *
+ * Purpose:     Check if the object at obj_oloc is or contains a reference
+ *              to a committed datatype.  If it does, adds it to the merge
+ *              committed dt skiplist present in udata if it does not match
+ *              any already present.
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Nov 3 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_copy_search_comm_dt_check(H5O_loc_t *obj_oloc,
+    H5O_copy_search_comm_dt_ud_t *udata)
+{
+    H5O_copy_search_comm_dt_key_t *key = NULL; /* Skiplist key */
+    haddr_t     *addr = NULL;           /* Destination address */
+    hbool_t     obj_inserted = FALSE;   /* Object inserted into skip list */
+    H5O_info_t  oinfo;                  /* Object info */
+    H5A_attr_iter_op_t attr_op;         /* Attribute iteration operator */
+    herr_t      ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    /* Sanity checks */
+    HDassert(obj_oloc);
+    HDassert(udata);
+    HDassert(udata->dst_dt_list);
+    HDassert(udata->dst_root_loc);
+
+    /* Get the object's info */
+    if(H5O_get_info(obj_oloc, udata->dxpl_id, TRUE, &oinfo) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "unable to get object info")
+
+    /* Check if the object is a datatype, a dataset using a committed
+     * datatype, or contains an attribute using a committed datatype */
+    if(oinfo.type == H5O_TYPE_NAMED_DATATYPE) {
+        /* Allocate key */
+        if(NULL == (key = H5FL_MALLOC(H5O_copy_search_comm_dt_key_t)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+        /* Read the destination datatype */
+        if(NULL == (key->dt = (H5T_t *)H5O_msg_read(obj_oloc, H5O_DTYPE_ID, NULL, udata->dxpl_id)))
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't read DTYPE message")
+
+        /* Get destination object fileno */
+        H5F_GET_FILENO(obj_oloc->file, key->fileno);
+
+        /* Check if the datatype is already present in the skip list */
+        if(!H5SL_search(udata->dst_dt_list, key)) {
+            /* Allocate destination address */
+            if(NULL == (addr = H5FL_MALLOC(haddr_t)))
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+            /* Add the destination datatype to the skip list */
+            *addr = obj_oloc->addr;
+            if(H5SL_insert(udata->dst_dt_list, addr, key) < 0)
+                HGOTO_ERROR(H5E_OHDR, H5E_CANTINSERT, FAIL, "can't insert object into skip list")
+            obj_inserted = TRUE;
+        } /* end if */
+    } /* end if */
+    else if(oinfo.type == H5O_TYPE_DATASET) {
+        /* Allocate key */
+        if(NULL == (key = H5FL_MALLOC(H5O_copy_search_comm_dt_key_t)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+        /* Read the destination datatype */
+        if(NULL == (key->dt = (H5T_t *)H5O_msg_read(obj_oloc, H5O_DTYPE_ID, NULL, udata->dxpl_id)))
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't read DTYPE message")
+
+        /* Check if the datatype is committed and search the skip list if so
+            */
+        if(H5T_committed(key->dt)) {
+            /* Get datatype object fileno */
+            H5F_GET_FILENO(obj_oloc->file, key->fileno);
+
+            if(!H5SL_search(udata->dst_dt_list, key)) {
+                /* Allocate destination address */
+                if(NULL == (addr = H5FL_MALLOC(haddr_t)))
+                    HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+                /* Add the destination datatype to the skip list */
+                *addr = ((H5O_shared_t *)(key->dt))->u.loc.oh_addr;
+                if(H5SL_insert(udata->dst_dt_list, addr, key) < 0)
+                    HGOTO_ERROR(H5E_OHDR, H5E_CANTINSERT, FAIL, "can't insert object into skip list")
+                obj_inserted = TRUE;
+            } /* end if */
+        } /* end if */
+    } /* end else */
+
+    /* Search within attributes */
+    attr_op.op_type = H5A_ATTR_OP_LIB;
+    attr_op.u.lib_op = H5O_copy_search_comm_dt_attr_cb;
+    udata->obj_oloc.file = obj_oloc->file;
+    udata->obj_oloc.addr = obj_oloc->addr;
+    if(H5O_attr_iterate_real((hid_t)-1, obj_oloc, udata->dxpl_id, H5_INDEX_NAME, H5_ITER_NATIVE, 0, NULL, &attr_op, udata) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_BADITER, FAIL, "error iterating over attributes");
+
+done:
+    /* Release resources */
+    if(!obj_inserted) {
+        if(key) {
+            if(key->dt)
+                key->dt = (H5T_t *)H5O_msg_free(H5O_DTYPE_ID, key->dt);
+            key = H5FL_FREE(H5O_copy_search_comm_dt_key_t, key);
+        } /* end if */
+        if(addr) {
+            HDassert(ret_value < 0);
+            addr = H5FL_FREE(haddr_t, addr);
+        } /* end if */
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_copy_search_comm_dt_check */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_copy_search_comm_dt_cb
+ *
+ * Purpose:     H5G_visit callback to add committed datatypes to the merge
+ *              committed dt skiplist.  Mostly a wrapper for
+ *              H5O_copy_search_comm_dt_check.
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Oct 6 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_copy_search_comm_dt_cb(hid_t UNUSED group, const char *name,
+    const H5L_info_t *linfo, void *_udata)
+{
+    H5O_copy_search_comm_dt_ud_t *udata = (H5O_copy_search_comm_dt_ud_t *)_udata; /* Skip list of dtypes in dest file */
+    H5G_loc_t   obj_loc;                /* Location of object */
+    H5O_loc_t   obj_oloc;               /* Object's object location */
+    H5G_name_t  obj_path;               /* Object's group hier. path */
+    hbool_t     obj_found = FALSE;      /* Object at 'name' found */
+    herr_t      ret_value = H5_ITER_CONT; /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    /* Sanity checks */
+    HDassert(name);
+    HDassert(linfo);
+    HDassert(udata);
+    HDassert(udata->dst_dt_list);
+    HDassert(udata->dst_root_loc);
+
+    /* Check if this is a hard link */
+    if(linfo->type == H5L_TYPE_HARD) {
+        /* Set up opened group location to fill in */
+        obj_loc.oloc = &obj_oloc;
+        obj_loc.path = &obj_path;
+        H5G_loc_reset(&obj_loc);
+
+        /* Find the object */
+        if(H5G_loc_find(udata->dst_root_loc, name, &obj_loc/*out*/, H5P_LINK_ACCESS_DEFAULT, udata->dxpl_id) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_NOTFOUND, H5_ITER_ERROR, "object not found")
+        obj_found = TRUE;
+
+        /* Check object and add to skip list if appropriate */
+        if(H5O_copy_search_comm_dt_check(&obj_oloc, udata) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, H5_ITER_ERROR, "can't check object")
+    } /* end if */
+
+done:
+    /* Release resources */
+    if(obj_found && H5G_loc_free(&obj_loc) < 0)
+        HDONE_ERROR(H5E_OHDR, H5E_CANTRELEASE, H5_ITER_ERROR, "can't free location")
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_copy_search_comm_dt_cb */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_copy_search_comm_dt
+ *
+ * Purpose:     Checks if the committed datatype present in oh_src matches any
+ *              in the destination file, building the destination file
+ *              skiplist as necessary.
+ *
+ * Return:      TRUE if a match is found in the destination file
+ *                      - oloc_dst will contain the address
+ *              FALSE if a match is not found
+ *              Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Sep 27 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+static htri_t
+H5O_copy_search_comm_dt(H5F_t *file_src, H5O_t *oh_src,
+    H5O_loc_t *oloc_dst/*in, out*/, hid_t dxpl_id, H5O_copy_t *cpy_info)
+{
+    H5O_copy_search_comm_dt_key_t *key = NULL; /* Skiplist key */
+    haddr_t     *dst_addr;      /* Destination datatype address */
+    H5G_loc_t   dst_root_loc = {NULL, NULL}; /* Destination root group location */
+    H5O_copy_search_comm_dt_ud_t udata; /* Group iteration user data */
+    herr_t      ret_value = FALSE; /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    /* Sanity checks */
+    HDassert(oh_src);
+    HDassert(oloc_dst);
+    HDassert(oloc_dst->file);
+    HDassert(H5F_FILE_ID(oloc_dst->file) >= 0);
+    HDassert(cpy_info);
+
+    /* Allocate key */
+    if(NULL == (key = H5FL_MALLOC(H5O_copy_search_comm_dt_key_t)))
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+    /* Read the source datatype */
+    if(NULL == (key->dt = (H5T_t *)H5O_msg_read_oh(file_src, dxpl_id, oh_src, H5O_DTYPE_ID, NULL)))
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't read DTYPE message")
+
+    /* Get destination object fileno */
+    H5F_GET_FILENO(oloc_dst->file, key->fileno);
+
+    /* Check if the destination dtype list exists, create it if it does not */
+    if(!cpy_info->dst_dt_list) {
+        /* Create the skip list */
+        if(NULL == (cpy_info->dst_dt_list = H5SL_create(H5SL_TYPE_GENERIC, H5O_copy_comm_dt_cmp)))
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTCREATE, FAIL, "can't create skip list for committed datatypes")
+
+        /* Add suggested types to list, if they are present */
+        if(cpy_info->dst_dt_suggestion_list) {
+            H5O_copy_dtype_merge_list_t *suggestion = cpy_info->dst_dt_suggestion_list;
+            H5G_loc_t   obj_loc;                /* Location of object */
+            H5O_loc_t   obj_oloc;               /* Object's object location */
+            H5G_name_t  obj_path;               /* Object's group hier. path */
+
+            /* Set up the root group in the destination file */
+            if(NULL == (dst_root_loc.oloc = H5G_oloc(H5G_rootof(oloc_dst->file))))
+                HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "unable to get object location for root group")
+            if(NULL == (dst_root_loc.path = H5G_nameof(H5G_rootof(oloc_dst->file))))
+                HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "unable to get path for root group")
+
+            /* Set up opened group location to fill in */
+            obj_loc.oloc = &obj_oloc;
+            obj_loc.path = &obj_path;
+            H5G_loc_reset(&obj_loc);
+
+            /* Build udata */
+            udata.dst_dt_list = cpy_info->dst_dt_list;
+            udata.dst_root_loc = &dst_root_loc;
+            udata.obj_oloc.file = NULL;
+            udata.obj_oloc.addr = HADDR_UNDEF;
+            udata.dxpl_id = dxpl_id;
+
+            /* Walk through the list of datatype suggestions */
+            while(suggestion) {
+                /* Find the object */
+                if(H5G_loc_find(&dst_root_loc, suggestion->path, &obj_loc/*out*/, H5P_LINK_ACCESS_DEFAULT, dxpl_id) < 0)
+                    /* Ignore errors - i.e. suggestions not present in
+                     * destination file */
+                    H5E_clear_stack(NULL);
+                else
+                    /* Check object and add to skip list if appropriate */
+                    if(H5O_copy_search_comm_dt_check(&obj_oloc, &udata) < 0) {
+                        if(H5G_loc_free(&obj_loc) < 0)
+                            HERROR(H5E_OHDR, H5E_CANTRELEASE, "can't free location");
+                        HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't check object")
+                    } /* end if */
+
+                /* Free location */
+                if(H5G_loc_free(&obj_loc) < 0)
+                    HGOTO_ERROR(H5E_OHDR, H5E_CANTRELEASE, FAIL, "can't free location");
+
+                /* Advance the suggestion pointer */
+                suggestion = suggestion->next;
+            } /* end while */
+        } /* end if */
+    }
+
+    if(!cpy_info->dst_dt_list_complete) {
+        /* Search for the type in the destination file, and return its address
+         * if found, but only if the list is populated with and only with
+         * suggested types.  We will search complete lists later. */
+        if(cpy_info->dst_dt_suggestion_list
+                && NULL != (dst_addr = (haddr_t *)H5SL_search(
+                cpy_info->dst_dt_list, key))) {
+            oloc_dst->addr = *dst_addr;
+            ret_value = TRUE;
+        } /* end if */
+        else {
+            H5O_mcdt_search_ret_t search_cb_ret = H5O_MCDT_SEARCH_CONT;
+
+            /* Make callback to see if we should search destination file */
+            if(cpy_info->mcdt_cb)
+                if((search_cb_ret = cpy_info->mcdt_cb(cpy_info->mcdt_ud)) == H5O_MCDT_SEARCH_ERROR)
+                    HGOTO_ERROR(H5E_OHDR, H5E_CALLBACK, FAIL, "callback returned error")
+
+            if(search_cb_ret == H5O_MCDT_SEARCH_CONT) {
+                /* Build the complete dst dt list */
+                /* Set up the root group in the destination file, if necessary */
+                if(!dst_root_loc.oloc) {
+                    HDassert(!dst_root_loc.path);
+                    if(NULL == (dst_root_loc.oloc = H5G_oloc(H5G_rootof(oloc_dst->file))))
+                        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "unable to get object location for root group")
+                    if(NULL == (dst_root_loc.path = H5G_nameof(H5G_rootof(oloc_dst->file))))
+                        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "unable to get path for root group")
+                } /* end if */
+                else
+                    HDassert(dst_root_loc.path);
+
+                /* Build udata.  Note that this may be done twice in some cases, but
+                * it should be rare and should be cheaper on average than trying to
+                * keep track of whether it was done before. */
+                udata.dst_dt_list = cpy_info->dst_dt_list;
+                udata.dst_root_loc = &dst_root_loc;
+                udata.obj_oloc.file = NULL;
+                udata.obj_oloc.addr = HADDR_UNDEF;
+                udata.dxpl_id = dxpl_id;
+
+                /* Traverse the destination file, adding committed datatypes to the skip
+                * list */
+                if(H5G_visit(H5F_FILE_ID(oloc_dst->file), "/", H5_INDEX_NAME, H5_ITER_NATIVE, H5O_copy_search_comm_dt_cb, &udata, H5P_LINK_ACCESS_DEFAULT, dxpl_id) < 0)
+                    HGOTO_ERROR(H5E_OHDR, H5E_BADITER, FAIL, "object visitation failed")
+                cpy_info->dst_dt_list_complete = TRUE;
+            } /* end if */
+            else
+                if(search_cb_ret != H5O_MCDT_SEARCH_STOP)
+                    HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "unknown return value for callback")
+        } /* end if */
+    } /* end if */
+
+    /* Search for the type in the destination file, and return its address if
+     * found, but only if the list is complete */
+    if(cpy_info->dst_dt_list_complete) {
+        if(NULL != (dst_addr = (haddr_t *)H5SL_search(cpy_info->dst_dt_list, key))) {
+            oloc_dst->addr = *dst_addr;
+            ret_value = TRUE;
+        } /* end if */
+    } /* end if */
+
+done:
+    if(key) {
+        if(key->dt)
+            key->dt = (H5T_t *)H5O_msg_free(H5O_DTYPE_ID, key->dt);
+        key = H5FL_FREE(H5O_copy_search_comm_dt_key_t, key);
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_copy_search_comm_dt */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_copy_insert_comm_dt
+ *
+ * Purpose:     Insert the committed datatype at oloc_dst into the merge committed
+ *              dt skiplist.  The datatype must not be present already.
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Oct 6 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_copy_insert_comm_dt(H5F_t *file_src, H5O_t *oh_src, H5O_loc_t *oloc_dst,
+    hid_t dxpl_id, H5O_copy_t *cpy_info)
+{
+    H5O_copy_search_comm_dt_key_t *key = NULL; /* Skiplist key */
+    haddr_t     *addr = NULL;   /* Destination object address */
+    herr_t      ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    /* Sanity checks */
+    HDassert(oh_src);
+    HDassert(oloc_dst);
+    HDassert(oloc_dst->file);
+    HDassert(oloc_dst->addr != HADDR_UNDEF);
+    HDassert(cpy_info);
+    HDassert(cpy_info->dst_dt_list);
+
+    /* Allocate key */
+    if(NULL == (key = H5FL_MALLOC(H5O_copy_search_comm_dt_key_t)))
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+    /* Read the datatype.  Read from the source file because the destination
+     * object could be changed in the post-copy. */
+    if(NULL == (key->dt = (H5T_t *)H5O_msg_read_oh(file_src, dxpl_id, oh_src, H5O_DTYPE_ID, NULL)))
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't read DTYPE message")
+
+    /* Get destination object fileno */
+    H5F_GET_FILENO(oloc_dst->file, key->fileno);
+
+    /* Allocate destination address */
+    if(NULL == (addr = H5FL_MALLOC(haddr_t)))
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+    /* Add the destination datatype to the skip list */
+    *addr = oloc_dst->addr;
+    if(H5SL_insert(cpy_info->dst_dt_list, addr, key) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTINSERT, FAIL, "can't insert object into skip list")
+
+done:
+    if(ret_value < 0) {
+        if(key) {
+            if(key->dt)
+                key->dt = (H5T_t *)H5O_msg_free(H5O_DTYPE_ID, key->dt);
+            key = H5FL_FREE(H5O_copy_search_comm_dt_key_t, key);
+        } /* end if */
+        if(addr)
+            addr = H5FL_FREE(haddr_t, addr);
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_copy_insert_comm_dt */
+
diff --git a/src/H5Odtype.c b/src/H5Odtype.c
index 9ccb51b..1b602c7 100644
--- a/src/H5Odtype.c
+++ b/src/H5Odtype.c
@@ -43,6 +43,9 @@ static herr_t H5O_dtype_pre_copy_file(H5F_t *file_src, const void *mesg_src,
 static void *H5O_dtype_copy_file(H5F_t *file_src, const H5O_msg_class_t *mesg_type,
     void *native_src, H5F_t *file_dst, hbool_t *recompute_size,
     H5O_copy_t *cpy_info, void *udata, hid_t dxpl_id);
+static herr_t H5O_dtype_shared_post_copy_upd(const H5O_loc_t *src_oloc,
+    const void *mesg_src, H5O_loc_t *dst_oloc, void *mesg_dst, hid_t dxpl_id,
+    H5O_copy_t *cpy_info);
 
 static herr_t H5O_dtype_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg,
     FILE * stream, int indent, int fwidth);
@@ -63,6 +66,7 @@ static herr_t H5O_dtype_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg,
 #define H5O_SHARED_COPY_FILE_REAL	H5O_dtype_copy_file
 #define H5O_SHARED_POST_COPY_FILE	H5O_dtype_shared_post_copy_file
 #undef  H5O_SHARED_POST_COPY_FILE_REAL
+#define H5O_SHARED_POST_COPY_FILE_UPD   H5O_dtype_shared_post_copy_upd
 #define H5O_SHARED_DEBUG		H5O_dtype_shared_debug
 #define H5O_SHARED_DEBUG_REAL		H5O_dtype_debug
 #include "H5Oshared.h"			/* Shared Object Header Message Callbacks */
@@ -1575,6 +1579,40 @@ done:
 } /* end H5O_dtype_copy_file() */
 
 
+/*-------------------------------------------------------------------------
+ * Function:    H5O_dtype_shared_post_copy_upd
+ *
+ * Purpose:     Update a message after the shared message operations
+ *              during the post-copy loop
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              November 8, 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_dtype_shared_post_copy_upd(const H5O_loc_t UNUSED *src_oloc,
+    const void UNUSED *mesg_src, H5O_loc_t UNUSED *dst_oloc, void *mesg_dst,
+    hid_t UNUSED dxpl_id, H5O_copy_t UNUSED *cpy_info)
+{
+    H5T_t       *dt_dst = (H5T_t *)mesg_dst;    /* Destination datatype */
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    if(dt_dst->sh_loc.type == H5O_SHARE_TYPE_COMMITTED) {
+        HDassert(H5T_committed(dt_dst));
+        dt_dst->oloc.file = dt_dst->sh_loc.file;
+        dt_dst->oloc.addr = dt_dst->sh_loc.u.loc.oh_addr;
+    } /* end if */
+    else
+        HDassert(!H5T_committed(dt_dst));
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5O_dtype_shared_post_copy_upd */
+
+
 /*--------------------------------------------------------------------------
  NAME
     H5O_dtype_debug
diff --git a/src/H5Oefl.c b/src/H5Oefl.c
index b71af5e..c8b6d01 100644
--- a/src/H5Oefl.c
+++ b/src/H5Oefl.c
@@ -36,8 +36,8 @@ static void *H5O_efl_copy(const void *_mesg, void *_dest);
 static size_t H5O_efl_size(const H5F_t *f, hbool_t disable_shared, const void *_mesg);
 static herr_t H5O_efl_reset(void *_mesg);
 static void *H5O_efl_copy_file(H5F_t *file_src, void *mesg_src,
-    H5F_t *file_dst, hbool_t *recompute_size, H5O_copy_t *cpy_info,
-    void *udata, hid_t dxpl_id);
+    H5F_t *file_dst, hbool_t *recompute_size, unsigned *mesg_flags,
+    H5O_copy_t *cpy_info, void *udata, hid_t dxpl_id);
 static herr_t H5O_efl_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg, FILE * stream,
 			    int indent, int fwidth);
 
@@ -455,8 +455,8 @@ done:
  */
 static void *
 H5O_efl_copy_file(H5F_t UNUSED *file_src, void *mesg_src, H5F_t *file_dst,
-    hbool_t UNUSED *recompute_size, H5O_copy_t UNUSED *cpy_info,
-    void UNUSED *_udata, hid_t dxpl_id)
+    hbool_t UNUSED *recompute_size, unsigned UNUSED *mesg_flags,
+    H5O_copy_t UNUSED *cpy_info, void UNUSED *_udata, hid_t dxpl_id)
 {
     H5O_efl_t   *efl_src = (H5O_efl_t *) mesg_src;
     H5O_efl_t   *efl_dst = NULL;
diff --git a/src/H5Ofill.c b/src/H5Ofill.c
index 9fa6108..f5569dc 100644
--- a/src/H5Ofill.c
+++ b/src/H5Ofill.c
@@ -63,6 +63,7 @@ static herr_t H5O_fill_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg, FILE *s
 #undef H5O_SHARED_COPY_FILE_REAL
 #define H5O_SHARED_POST_COPY_FILE	H5O_fill_shared_post_copy_file
 #undef H5O_SHARED_POST_COPY_FILE_REAL
+#undef  H5O_SHARED_POST_COPY_FILE_UPD
 #define H5O_SHARED_DEBUG		H5O_fill_shared_debug
 #define H5O_SHARED_DEBUG_REAL		H5O_fill_debug
 #include "H5Oshared.h"			/* Shared Object Header Message Callbacks */
@@ -95,6 +96,7 @@ static herr_t H5O_fill_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg, FILE *s
 #undef H5O_SHARED_POST_COPY_FILE
 #define H5O_SHARED_POST_COPY_FILE	H5O_fill_new_shared_post_copy_file
 #undef H5O_SHARED_POST_COPY_FILE_REAL
+#undef  H5O_SHARED_POST_COPY_FILE_UPD
 #undef H5O_SHARED_DEBUG
 #define H5O_SHARED_DEBUG		H5O_fill_new_shared_debug
 #undef H5O_SHARED_DEBUG_REAL
diff --git a/src/H5Olayout.c b/src/H5Olayout.c
index 1b17bff..e912d8c 100644
--- a/src/H5Olayout.c
+++ b/src/H5Olayout.c
@@ -46,8 +46,8 @@ static herr_t H5O_layout_free(void *_mesg);
 static herr_t H5O_layout_delete(H5F_t *f, hid_t dxpl_id, H5O_t *open_oh,
     void *_mesg);
 static void *H5O_layout_copy_file(H5F_t *file_src, void *mesg_src,
-    H5F_t *file_dst, hbool_t *recompute_size, H5O_copy_t *cpy_info,
-    void *udata, hid_t dxpl_id);
+    H5F_t *file_dst, hbool_t *recompute_size, unsigned *mesg_flags,
+    H5O_copy_t *cpy_info, void *udata, hid_t dxpl_id);
 static herr_t H5O_layout_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg, FILE * stream,
 			       int indent, int fwidth);
 
@@ -587,8 +587,8 @@ done:
  */
 static void *
 H5O_layout_copy_file(H5F_t *file_src, void *mesg_src, H5F_t *file_dst,
-    hbool_t UNUSED *recompute_size, H5O_copy_t *cpy_info, void *_udata,
-    hid_t dxpl_id)
+    hbool_t UNUSED *recompute_size, unsigned UNUSED *mesg_flags,
+    H5O_copy_t *cpy_info, void *_udata, hid_t dxpl_id)
 {
     H5D_copy_file_ud_t *udata = (H5D_copy_file_ud_t *)_udata;   /* Dataset copying user data */
     H5O_layout_t       *layout_src = (H5O_layout_t *) mesg_src;
diff --git a/src/H5Olinfo.c b/src/H5Olinfo.c
index 4939bab..8eabc1b 100644
--- a/src/H5Olinfo.c
+++ b/src/H5Olinfo.c
@@ -46,10 +46,11 @@ static herr_t H5O_linfo_free(void *_mesg);
 static herr_t H5O_linfo_delete(H5F_t *f, hid_t dxpl_id, H5O_t *open_oh,
     void *_mesg);
 static void *H5O_linfo_copy_file(H5F_t *file_src, void *native_src,
-    H5F_t *file_dst, hbool_t *recompute_size, H5O_copy_t *cpy_info,
-    void *udata, hid_t dxpl_id);
-static herr_t H5O_linfo_post_copy_file(const H5O_loc_t *parent_src_oloc, const void *mesg_src, H5O_loc_t *dst_oloc,
-    void *mesg_dst, hid_t dxpl_id, H5O_copy_t *cpy_info);
+    H5F_t *file_dst, hbool_t *recompute_size, unsigned *mesg_flags,
+    H5O_copy_t *cpy_info, void *udata, hid_t dxpl_id);
+static herr_t H5O_linfo_post_copy_file(const H5O_loc_t *parent_src_oloc,
+    const void *mesg_src, H5O_loc_t *dst_oloc, void *mesg_dst,
+    unsigned *mesg_flags, hid_t dxpl_id, H5O_copy_t *cpy_info);
 static herr_t H5O_linfo_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg,
 			     FILE * stream, int indent, int fwidth);
 
@@ -379,8 +380,8 @@ done:
  */
 static void *
 H5O_linfo_copy_file(H5F_t UNUSED *file_src, void *native_src, H5F_t *file_dst,
-    hbool_t UNUSED *recompute_size, H5O_copy_t *cpy_info, void *_udata,
-    hid_t dxpl_id)
+    hbool_t UNUSED *recompute_size, unsigned UNUSED *mesg_flags,
+    H5O_copy_t *cpy_info, void *_udata, hid_t dxpl_id)
 {
     H5O_linfo_t          *linfo_src = (H5O_linfo_t *) native_src;
     H5O_linfo_t          *linfo_dst = NULL;
@@ -495,7 +496,8 @@ done:
  */
 static herr_t
 H5O_linfo_post_copy_file(const H5O_loc_t *src_oloc, const void *mesg_src,
-    H5O_loc_t *dst_oloc, void *mesg_dst, hid_t dxpl_id, H5O_copy_t *cpy_info)
+    H5O_loc_t *dst_oloc, void *mesg_dst, unsigned UNUSED *mesg_flags,
+    hid_t dxpl_id, H5O_copy_t *cpy_info)
 {
     const H5O_linfo_t   *linfo_src = (const H5O_linfo_t *)mesg_src;
     H5O_linfo_t         *linfo_dst = (H5O_linfo_t *)mesg_dst;
diff --git a/src/H5Olink.c b/src/H5Olink.c
index ccc6d0e..88c9e28 100644
--- a/src/H5Olink.c
+++ b/src/H5Olink.c
@@ -49,10 +49,11 @@ static herr_t H5O_link_free(void *_mesg);
 static herr_t H5O_link_pre_copy_file(H5F_t *file_src, const void *mesg_src,
     hbool_t *deleted, const H5O_copy_t *cpy_info, void *udata);
 static void *H5O_link_copy_file(H5F_t *file_src, void *native_src,
-    H5F_t *file_dst, hbool_t *recompute_size, H5O_copy_t *cpy_info, void *udata,
-    hid_t dxpl_id);
-static herr_t H5O_link_post_copy_file(const H5O_loc_t *src_oloc, const void *mesg_src, H5O_loc_t *dst_oloc,
-    void *mesg_dst, hid_t dxpl_id, H5O_copy_t *cpy_info);
+    H5F_t *file_dst, hbool_t *recompute_size, unsigned *mesg_flags,
+    H5O_copy_t *cpy_info, void *udata, hid_t dxpl_id);
+static herr_t H5O_link_post_copy_file(const H5O_loc_t *src_oloc,
+    const void *mesg_src, H5O_loc_t *dst_oloc, void *mesg_dst,
+    unsigned *mesg_flags, hid_t dxpl_id, H5O_copy_t *cpy_info);
 static herr_t H5O_link_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg,
     FILE * stream, int indent, int fwidth);
 
@@ -710,8 +711,8 @@ H5O_link_pre_copy_file(H5F_t UNUSED *file_src, const void UNUSED *native_src,
  */
 static void *
 H5O_link_copy_file(H5F_t UNUSED *file_src, void *native_src, H5F_t UNUSED *file_dst,
-    hbool_t UNUSED *recompute_size, H5O_copy_t UNUSED *cpy_info, void UNUSED *udata,
-    hid_t UNUSED dxpl_id)
+    hbool_t UNUSED *recompute_size, unsigned UNUSED *mesg_flags,
+    H5O_copy_t UNUSED *cpy_info, void UNUSED *udata, hid_t UNUSED dxpl_id)
 {
     H5O_link_t  *link_src = (H5O_link_t *)native_src;
     void        *ret_value;          /* Return value */
@@ -751,7 +752,8 @@ done:
  */
 static herr_t
 H5O_link_post_copy_file(const H5O_loc_t *src_oloc, const void *mesg_src,
-    H5O_loc_t *dst_oloc, void *mesg_dst, hid_t dxpl_id, H5O_copy_t *cpy_info)
+    H5O_loc_t *dst_oloc, void *mesg_dst, unsigned UNUSED *mesg_flags,
+    hid_t dxpl_id, H5O_copy_t *cpy_info)
 {
     const H5O_link_t    *link_src = (const H5O_link_t *)mesg_src;
     H5O_link_t          *link_dst = (H5O_link_t *)mesg_dst;
diff --git a/src/H5Omessage.c b/src/H5Omessage.c
index 8d1c318..48461fc 100644
--- a/src/H5Omessage.c
+++ b/src/H5Omessage.c
@@ -1865,7 +1865,7 @@ done:
 void *
 H5O_msg_copy_file(const H5O_msg_class_t *type, H5F_t *file_src,
     void *native_src, H5F_t *file_dst, hbool_t *recompute_size,
-    H5O_copy_t *cpy_info, void *udata, hid_t dxpl_id)
+    unsigned *mesg_flags, H5O_copy_t *cpy_info, void *udata, hid_t dxpl_id)
 {
     void        *ret_value;
 
@@ -1883,7 +1883,7 @@ H5O_msg_copy_file(const H5O_msg_class_t *type, H5F_t *file_src,
     /* The copy_file callback will return an H5O_shared_t only if the message
      * to be copied is a committed datatype.
      */
-    if(NULL == (ret_value = (type->copy_file)(file_src, native_src, file_dst, recompute_size, cpy_info, udata, dxpl_id)))
+    if(NULL == (ret_value = (type->copy_file)(file_src, native_src, file_dst, recompute_size, mesg_flags, cpy_info, udata, dxpl_id)))
         HGOTO_ERROR(H5E_OHDR, H5E_CANTCOPY, NULL, "unable to copy object header message to file")
 
 done:
@@ -1996,7 +1996,7 @@ H5O_copy_mesg(H5F_t *f, hid_t dxpl_id, H5O_t *oh, unsigned idx,
         HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to copy message to object header")
 
     /* Update the message flags */
-    idx_msg->flags = mesg_flags;
+    idx_msg->flags = (uint8_t)mesg_flags;
 
     /* Mark the message as modified */
     idx_msg->dirty = TRUE;
diff --git a/src/H5Opkg.h b/src/H5Opkg.h
index 34a413c..1b612fc 100644
--- a/src/H5Opkg.h
+++ b/src/H5Opkg.h
@@ -234,8 +234,8 @@ struct H5O_msg_class_t {
     herr_t	(*set_share)(void*, const H5O_shared_t*);   /* Set shared information */
     htri_t	(*can_share)(const void *);	/* Is message allowed to be shared? */
     herr_t	(*pre_copy_file)(H5F_t *, const void *, hbool_t *, const H5O_copy_t *, void *); /*"pre copy" action when copying native value to file */
-    void	*(*copy_file)(H5F_t *, void *, H5F_t *, hbool_t *, H5O_copy_t *, void *, hid_t); /*copy native value to file */
-    herr_t	(*post_copy_file)(const H5O_loc_t *, const void *, H5O_loc_t *, void *, hid_t, H5O_copy_t *); /*"post copy" action when copying native value to file */
+    void	*(*copy_file)(H5F_t *, void *, H5F_t *, hbool_t *, unsigned *, H5O_copy_t *, void *, hid_t); /*copy native value to file */
+    herr_t	(*post_copy_file)(const H5O_loc_t *, const void *, H5O_loc_t *, void *, unsigned *, hid_t, H5O_copy_t *); /*"post copy" action when copying native value to file */
     herr_t      (*get_crt_index)(const void *, H5O_msg_crt_idx_t *);	/* Get message's creation index */
     herr_t      (*set_crt_index)(void *, H5O_msg_crt_idx_t);	/* Set message's creation index */
     herr_t	(*debug)(H5F_t*, hid_t, const void*, FILE*, int, int);
@@ -546,7 +546,7 @@ H5_DLL herr_t H5O_msg_remove_real(H5F_t *f, H5O_t *oh, const H5O_msg_class_t *ty
     int sequence, H5O_operator_t op, void *op_data, hbool_t adj_link, hid_t dxpl_id);
 H5_DLL void *H5O_msg_copy_file(const H5O_msg_class_t *type, H5F_t *file_src,
     void *mesg_src, H5F_t *file_dst, hbool_t *recompute_size,
-    H5O_copy_t *cpy_info, void *udata, hid_t dxpl_id);
+    unsigned *mesg_flags, H5O_copy_t *cpy_info, void *udata, hid_t dxpl_id);
 H5_DLL herr_t H5O_msg_iterate_real(H5F_t *f, H5O_t *oh, const H5O_msg_class_t *type,
     const H5O_mesg_operator_t *op, void *op_data, hid_t dxpl_id);
 
@@ -583,10 +583,12 @@ H5_DLL herr_t H5O_shared_link(H5F_t *f, hid_t dxpl_id, H5O_t *open_oh,
     const H5O_msg_class_t *mesg_type, H5O_shared_t *sh_mesg);
 H5_DLL herr_t H5O_shared_copy_file(H5F_t *file_src, H5F_t *file_dst,
     const H5O_msg_class_t *mesg_type, const void *_native_src, void *_native_dst,
-    hbool_t *recompute_size, H5O_copy_t *cpy_info, void *udata, hid_t dxpl_id);
+    hbool_t *recompute_size, unsigned *mesg_flags, H5O_copy_t *cpy_info,
+    void *udata, hid_t dxpl_id);
 H5_DLL herr_t H5O_shared_post_copy_file (H5F_t *f,
     const H5O_msg_class_t *mesg_type, const H5O_shared_t *shared_src,
-    H5O_shared_t *shared_dst, hid_t dxpl_id, H5O_copy_t *cpy_info);
+    H5O_shared_t *shared_dst, unsigned *mesg_flags, hid_t dxpl_id,
+    H5O_copy_t *cpy_info);
 H5_DLL herr_t H5O_shared_debug(const H5O_shared_t *mesg, FILE *stream,
     int indent, int fwidth);
 
diff --git a/src/H5Opline.c b/src/H5Opline.c
index 89ce865..f626106 100644
--- a/src/H5Opline.c
+++ b/src/H5Opline.c
@@ -61,6 +61,7 @@ static herr_t H5O_pline_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg,
 #undef H5O_SHARED_COPY_FILE_REAL
 #define H5O_SHARED_POST_COPY_FILE	H5O_pline_shared_post_copy_file
 #undef H5O_SHARED_POST_COPY_FILE_REAL
+#undef  H5O_SHARED_POST_COPY_FILE_UPD
 #define H5O_SHARED_DEBUG		H5O_pline_shared_debug
 #define H5O_SHARED_DEBUG_REAL		H5O_pline_debug
 #include "H5Oshared.h"			/* Shared Object Header Message Callbacks */
diff --git a/src/H5Oprivate.h b/src/H5Oprivate.h
index 2640dee..ae31932 100644
--- a/src/H5Oprivate.h
+++ b/src/H5Oprivate.h
@@ -99,7 +99,9 @@ typedef struct H5O_t H5O_t;
 #endif /* H5O_ENABLE_BAD_MESG_COUNT */
 
 /* ========= Object Copy properties ============ */
-#define H5O_CPY_OPTION_NAME 		"copy object"           /* Copy options */
+#define H5O_CPY_OPTION_NAME 		 "copy object"           /* Copy options */
+#define H5O_CPY_MERGE_COMM_DT_LIST_NAME "merge committed dtype list"   /* List of datatype paths to search in the dest file for merging */
+#define H5O_CPY_MCDT_SEARCH_CB_NAME 	 "committed dtype list search" /* Callback function when the search for a matching committed datatype is complete */
 
 /* If the module using this macro is allowed access to the private variables, access them directly */
 #ifdef H5O_PACKAGE
@@ -133,6 +135,18 @@ typedef struct H5O_loc_t {
                                  * its file's count of open objects. */
 } H5O_loc_t;
 
+/* Typedef for linked list of datatype merge suggestions */
+typedef struct H5O_copy_dtype_merge_list_t {
+    char *path; /* Path to datatype in destination file */
+    struct H5O_copy_dtype_merge_list_t *next; /* Next object in list */
+} H5O_copy_dtype_merge_list_t;
+
+/* Structure for callback property before searching the global list of committed datatypes at destination */
+typedef struct H5O_mcdt_cb_info_t {
+    H5O_mcdt_search_cb_t 	func;
+    void  			*user_data;
+} H5O_mcdt_cb_info_t;
+
 /* Settings/flags for copying an object */
 typedef struct H5O_copy_t {
     hbool_t copy_shallow;               /* Flag to perform shallow hierarchy copy */
@@ -141,10 +155,16 @@ typedef struct H5O_copy_t {
     hbool_t expand_ref;                 /* Flag to expand object references */
     hbool_t copy_without_attr;          /* Flag to not copy attributes */
     hbool_t preserve_null;              /* Flag to not delete NULL messages */
+    hbool_t merge_comm_dt;             /* Flag to merge committed datatypes in dest file */
+    H5O_copy_dtype_merge_list_t *dst_dt_suggestion_list; /* Suggestions for merging committed datatypes */
     int     curr_depth;                 /* Current depth in hierarchy copied */
     int     max_depth;                  /* Maximum depth in hierarchy to copy */
     H5SL_t  *map_list;                  /* Skip list to hold address mappings */
+    H5SL_t  *dst_dt_list;               /* Skip list to hold committed datatypes in dest file */
+    hbool_t dst_dt_list_complete;       /* Whether the destination datatype list is complete (i.e. not only populated with "suggestions" from H5Padd_merge_committed_dtype_path) */
     H5O_t   *oh_dst;                    /* The destination object header */
+    H5O_mcdt_search_cb_t mcdt_cb;	/* The callback to invoke before searching the global list of committed datatypes at destination */
+    void *mcdt_ud;			/* User data passed to callback */
 } H5O_copy_t;
 
 /* Header message IDs */
diff --git a/src/H5Opublic.h b/src/H5Opublic.h
index c5ae3c1..32945e8 100644
--- a/src/H5Opublic.h
+++ b/src/H5Opublic.h
@@ -43,7 +43,8 @@
 #define H5O_COPY_EXPAND_REFERENCE_FLAG	(0x0008u)   /* Copy objects that are pointed by references */
 #define H5O_COPY_WITHOUT_ATTR_FLAG      (0x0010u)   /* Copy object without copying attributes */
 #define H5O_COPY_PRESERVE_NULL_FLAG     (0x0020u)   /* Copy NULL messages (empty space) */
-#define H5O_COPY_ALL                    (0x003Fu)   /* All object copying flags (for internal checking) */
+#define H5O_COPY_MERGE_COMMITTED_DTYPE_FLAG (0x0040u)   /* Merge committed datatypes in dest file */
+#define H5O_COPY_ALL                    (0x007Fu)   /* All object copying flags (for internal checking) */
 
 /* Flags for shared message indexes.
  * Pass these flags in using the mesg_type_flags parameter in
@@ -131,6 +132,14 @@ typedef uint32_t H5O_msg_crt_idx_t;
 typedef herr_t (*H5O_iterate_t)(hid_t obj, const char *name, const H5O_info_t *info,
     void *op_data);
 
+typedef enum H5O_mcdt_search_ret_t {
+    H5O_MCDT_SEARCH_ERROR = -1,	/* Abort H5Ocopy */
+    H5O_MCDT_SEARCH_CONT,	/* Continue the global search of all committed datatypes in the destination file */
+    H5O_MCDT_SEARCH_STOP	/* Stop the search, but continue copying.  The committed datatype will be copied but not merged. */
+} H5O_mcdt_search_ret_t;
+
+/* Callback to invoke when completing the search for a matching committed datatype from the committed dtype list */
+typedef H5O_mcdt_search_ret_t (*H5O_mcdt_search_cb_t)(void *op_data);
 
 /********************/
 /* Public Variables */
diff --git a/src/H5Osdspace.c b/src/H5Osdspace.c
index 8ae73f7..905c4e9 100644
--- a/src/H5Osdspace.c
+++ b/src/H5Osdspace.c
@@ -55,6 +55,7 @@ static herr_t H5O_sdspace_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg,
 #undef H5O_SHARED_COPY_FILE_REAL
 #define H5O_SHARED_POST_COPY_FILE	H5O_sdspace_shared_post_copy_file
 #undef H5O_SHARED_POST_COPY_FILE_REAL
+#undef  H5O_SHARED_POST_COPY_FILE_UPD
 #define H5O_SHARED_DEBUG		H5O_sdspace_shared_debug
 #define H5O_SHARED_DEBUG_REAL		H5O_sdspace_debug
 #include "H5Oshared.h"			/* Shared Object Header Message Callbacks */
diff --git a/src/H5Oshared.c b/src/H5Oshared.c
index 45c0a7d..8a18c4a 100644
--- a/src/H5Oshared.c
+++ b/src/H5Oshared.c
@@ -589,8 +589,8 @@ done:
 herr_t
 H5O_shared_copy_file(H5F_t *file_src, H5F_t *file_dst,
     const H5O_msg_class_t *mesg_type, const void *_native_src, void *_native_dst,
-    hbool_t UNUSED *recompute_size, H5O_copy_t *cpy_info, void UNUSED *udata,
-    hid_t dxpl_id)
+    hbool_t UNUSED *recompute_size, unsigned *mesg_flags, H5O_copy_t *cpy_info,
+    void UNUSED *udata, hid_t dxpl_id)
 {
     const H5O_shared_t  *shared_src = (const H5O_shared_t *)_native_src; /* Alias to shared info in native source */
     H5O_shared_t        *shared_dst = (H5O_shared_t *)_native_dst; /* Alias to shared info in native destination message */
@@ -618,13 +618,15 @@ H5O_shared_copy_file(H5F_t *file_src, H5F_t *file_dst,
      */
     if(shared_src->type != H5O_SHARE_TYPE_COMMITTED) {
         /* Simulate trying to share new message in the destination file. */
-        if(H5SM_try_share(file_dst, dxpl_id, NULL, H5SM_DEFER, mesg_type->id, _native_dst, NULL) < 0)
+        if(H5SM_try_share(file_dst, dxpl_id, NULL, H5SM_DEFER, mesg_type->id, _native_dst, mesg_flags) < 0)
             HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "unable to determine if message should be shared")
     } /* end if */
-    else
+    else {
         /* Mark the message as committed - as it will be committed in post copy
          */
         H5O_UPDATE_SHARED(shared_dst, H5O_SHARE_TYPE_COMMITTED, file_dst, mesg_type->id, 0, HADDR_UNDEF)
+        *mesg_flags |= H5O_MSG_FLAG_SHARED;
+    } /* end else */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -651,8 +653,8 @@ done:
  */
 herr_t
 H5O_shared_post_copy_file(H5F_t *f, const H5O_msg_class_t *mesg_type,
-    const H5O_shared_t *shared_src, H5O_shared_t *shared_dst, hid_t dxpl_id,
-    H5O_copy_t *cpy_info)
+    const H5O_shared_t *shared_src, H5O_shared_t *shared_dst,
+    unsigned *mesg_flags, hid_t dxpl_id, H5O_copy_t *cpy_info)
 {
     herr_t ret_value = SUCCEED;         /* Return value */
 
@@ -669,6 +671,7 @@ H5O_shared_post_copy_file(H5F_t *f, const H5O_msg_class_t *mesg_type,
         H5O_loc_t src_oloc;
 
         /* Copy the shared object from source to destination */
+        H5O_loc_reset(&dst_oloc);
         dst_oloc.file = f;
         src_oloc.file = shared_src->file;
         src_oloc.addr = shared_src->u.loc.oh_addr;
@@ -682,7 +685,7 @@ H5O_shared_post_copy_file(H5F_t *f, const H5O_msg_class_t *mesg_type,
     else
         /* Share the message */
         if(H5SM_try_share(f, dxpl_id, NULL, H5SM_WAS_DEFERRED, mesg_type->id,
-                shared_dst, NULL) < 0)
+                shared_dst, mesg_flags) < 0)
             HGOTO_ERROR(H5E_OHDR, H5E_BADMESG, FAIL, "can't share message")
 
 done:
diff --git a/src/H5Oshared.h b/src/H5Oshared.h
index ddacc25..3ec5709 100644
--- a/src/H5Oshared.h
+++ b/src/H5Oshared.h
@@ -320,7 +320,8 @@ done:
  */
 static H5_inline void *
 H5O_SHARED_COPY_FILE(H5F_t *file_src, void *_native_src, H5F_t *file_dst,
-    hbool_t *recompute_size, H5O_copy_t *cpy_info, void *udata, hid_t dxpl_id)
+    hbool_t *recompute_size, unsigned *mesg_flags, H5O_copy_t *cpy_info,
+    void *udata, hid_t dxpl_id)
 {
     void *dst_mesg = NULL;      /* Destination message */
     void *ret_value;            /* Return value */
@@ -348,8 +349,8 @@ H5O_SHARED_COPY_FILE(H5F_t *file_src, void *_native_src, H5F_t *file_dst,
     HDmemset(dst_mesg, 0, sizeof(H5O_shared_t));
 
     /* Handle sharing destination message */
-    if(H5O_shared_copy_file(file_src, file_dst, H5O_SHARED_TYPE,
-            _native_src, dst_mesg, recompute_size, cpy_info, udata, dxpl_id) < 0)
+    if(H5O_shared_copy_file(file_src, file_dst, H5O_SHARED_TYPE, _native_src,
+            dst_mesg, recompute_size, mesg_flags, cpy_info, udata, dxpl_id) < 0)
         HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, NULL, "unable to determine if message should be shared")
 
     /* Set return value */
@@ -383,7 +384,8 @@ done:
  */
 static H5_inline herr_t
 H5O_SHARED_POST_COPY_FILE(const H5O_loc_t *oloc_src, const void *mesg_src,
-    H5O_loc_t *oloc_dst, void *mesg_dst, hid_t dxpl_id, H5O_copy_t *cpy_info)
+    H5O_loc_t *oloc_dst, void *mesg_dst, unsigned *mesg_flags, hid_t dxpl_id,
+    H5O_copy_t *cpy_info)
 {
     const H5O_shared_t  *shared_src = (const H5O_shared_t *)mesg_src; /* Alias to shared info in native source */
     H5O_shared_t        *shared_dst = (H5O_shared_t *)mesg_dst; /* Alias to shared info in native destination */
@@ -405,7 +407,7 @@ H5O_SHARED_POST_COPY_FILE(const H5O_loc_t *oloc_src, const void *mesg_src,
 #endif /* H5O_SHARED_POST_COPY_FILE */
 
 #ifdef H5O_SHARED_POST_COPY_FILE_REAL
-    /* Call native message's copy file callback to copy the message */
+    /* Call native message's post copy file callback to copy the message */
     if(H5O_SHARED_POST_COPY_FILE_REAL(oloc_src, mesg_src, oloc_dst, mesg_dst, dxpl_id, cpy_info) <0 )
         HGOTO_ERROR(H5E_OHDR, H5E_CANTCOPY, FAIL, "unable to copy native message to another file")
 #endif /* H5O_SHARED_POST_COPY_FILE_REAL */
@@ -414,9 +416,16 @@ H5O_SHARED_POST_COPY_FILE(const H5O_loc_t *oloc_src, const void *mesg_src,
      * production if the DEFER pass determined it will not be shared; debug mode
      * verifies that it is indeed the case */
     if(H5O_shared_post_copy_file(oloc_dst->file, H5O_SHARED_TYPE,
-            shared_src, shared_dst, dxpl_id, cpy_info) < 0)
+            shared_src, shared_dst, mesg_flags, dxpl_id, cpy_info) < 0)
         HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "unable to fix shared message in post copy")
 
+#ifdef H5O_SHARED_POST_COPY_FILE_UPD
+    /* Call native message's post copy file update callback to update the
+     * message */
+    if(H5O_SHARED_POST_COPY_FILE_UPD(oloc_src, mesg_src, oloc_dst, mesg_dst, dxpl_id, cpy_info) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTCOPY, FAIL, "unable to update native message")
+#endif /* H5O_SHARED_POST_COPY_FILE_UPD */
+
     /* Make sure that if the the source or destination is committed, both are
      * committed */
     HDassert((shared_src->type == H5O_SHARE_TYPE_COMMITTED)
diff --git a/src/H5Ostab.c b/src/H5Ostab.c
index c43a76b..bb0c22d 100644
--- a/src/H5Ostab.c
+++ b/src/H5Ostab.c
@@ -44,10 +44,11 @@ static size_t H5O_stab_size(const H5F_t *f, hbool_t disable_shared, const void *
 static herr_t H5O_stab_free(void *_mesg);
 static herr_t H5O_stab_delete(H5F_t *f, hid_t dxpl_id, H5O_t *open_oh, void *_mesg);
 static void *H5O_stab_copy_file(H5F_t *file_src, void *native_src,
-    H5F_t *file_dst, hbool_t *recompute_size, H5O_copy_t *cpy_info, void *_udata,
-    hid_t dxpl_id);
-static herr_t H5O_stab_post_copy_file(const H5O_loc_t *src_oloc, const void *mesg_src, H5O_loc_t *dst_oloc,
-    void *mesg_dst, hid_t dxpl_id, H5O_copy_t *cpy_info);
+    H5F_t *file_dst, hbool_t *recompute_size, unsigned *mesg_flags,
+    H5O_copy_t *cpy_info, void *_udata, hid_t dxpl_id);
+static herr_t H5O_stab_post_copy_file(const H5O_loc_t *src_oloc,
+    const void *mesg_src, H5O_loc_t *dst_oloc, void *mesg_dst,
+    unsigned *mesg_flags, hid_t dxpl_id, H5O_copy_t *cpy_info);
 static herr_t H5O_stab_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg,
     FILE * stream, int indent, int fwidth);
 
@@ -307,8 +308,8 @@ done:
  */
 static void *
 H5O_stab_copy_file(H5F_t *file_src, void *native_src, H5F_t *file_dst,
-    hbool_t UNUSED *recompute_size, H5O_copy_t UNUSED *cpy_info, void *_udata,
-    hid_t dxpl_id)
+    hbool_t UNUSED *recompute_size, unsigned UNUSED *mesg_flags,
+    H5O_copy_t UNUSED *cpy_info, void *_udata, hid_t dxpl_id)
 {
     H5O_stab_t          *stab_src = (H5O_stab_t *) native_src;
     H5O_stab_t          *stab_dst = NULL;
@@ -364,8 +365,9 @@ done:
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5O_stab_post_copy_file(const H5O_loc_t *src_oloc, const void *mesg_src, H5O_loc_t *dst_oloc,
-    void *mesg_dst, hid_t dxpl_id, H5O_copy_t *cpy_info)
+H5O_stab_post_copy_file(const H5O_loc_t *src_oloc, const void *mesg_src,
+    H5O_loc_t *dst_oloc, void *mesg_dst, unsigned UNUSED *mesg_flags,
+    hid_t dxpl_id, H5O_copy_t *cpy_info)
 {
     const H5O_stab_t    *stab_src = (const H5O_stab_t *)mesg_src;
     H5O_stab_t          *stab_dst = (H5O_stab_t *)mesg_dst;
diff --git a/src/H5Pdcpl.c b/src/H5Pdcpl.c
index 6a3067d..32793e6 100644
--- a/src/H5Pdcpl.c
+++ b/src/H5Pdcpl.c
@@ -392,7 +392,7 @@ H5P_dcrt_layout_cmp(const void *_layout1, const void *_layout2, size_t UNUSED si
 
     /* Sanity check */
     HDassert(layout1);
-    HDassert(layout1);
+    HDassert(layout2);
     HDassert(size == sizeof(H5O_layout_t));
 
     /* Check for different layout type */
diff --git a/src/H5Pocpypl.c b/src/H5Pocpypl.c
index af50d80..e61a0d7 100644
--- a/src/H5Pocpypl.c
+++ b/src/H5Pocpypl.c
@@ -35,7 +35,9 @@
 /***********/
 #include "H5private.h"		/* Generic Functions			*/
 #include "H5Eprivate.h"		/* Error handling		  	*/
+#include "H5FLprivate.h"        /* Free Lists                           */
 #include "H5Iprivate.h"		/* IDs			  		*/
+#include "H5MMprivate.h"        /* Memory management                    */
 #include "H5Ppkg.h"		/* Property lists		  	*/
 
 
@@ -47,7 +49,13 @@
 /* Definitions for copy options */
 #define H5O_CPY_OPTION_SIZE			sizeof(unsigned)
 #define H5O_CPY_OPTION_DEF			0
-
+/* Definitions for merge committed dtype list */
+#define H5O_CPY_MERGE_COMM_DT_LIST_SIZE        sizeof(char *)
+#define H5O_CPY_MERGE_COMM_DT_LIST_DEF         NULL
+#define H5O_CPY_MERGE_COMM_DT_LIST_CMP         H5P_ocpy_merge_comm_dt_list_cmp
+/* Definitions for callback function when completing the search for a matching committed datatype from the committed dtype list */
+#define H5O_CPY_MCDT_SEARCH_CB_SIZE           sizeof(H5O_mcdt_cb_info_t)
+#define H5O_CPY_MCDT_SEARCH_CB_DEF            {NULL,NULL} 
 
 /******************/
 /* Local Typedefs */
@@ -63,8 +71,17 @@
 /* Local Prototypes */
 /********************/
 
+/* General routines */
+static H5O_copy_dtype_merge_list_t *H5P_free_merge_comm_dtype_list(H5O_copy_dtype_merge_list_t *dt_list);
+
 /* Property class callbacks */
 static herr_t H5P_ocpy_reg_prop(H5P_genclass_t *pclass);
+static herr_t H5P_ocpy_copy(hid_t dst_plist_id, hid_t src_plist_id,
+    void *copy_data);
+static herr_t H5P_ocpy_close(hid_t ocpypl_id, void *close_data);
+
+/* Property callbacks */
+static int H5P_ocpy_merge_comm_dt_list_cmp(const void *value1, const void *value2, size_t size);
 
 
 /*********************/
@@ -80,9 +97,9 @@ const H5P_libclass_t H5P_CLS_OCPY[1] = {{
     H5P_ocpy_reg_prop,		/* Default property registration routine */
     NULL,		        /* Class creation callback      */
     NULL,		        /* Class creation callback info */
-    NULL,			/* Class copy callback          */
+    H5P_ocpy_copy,		/* Class copy callback          */
     NULL,		        /* Class copy callback info     */
-    NULL,			/* Class close callback         */
+    H5P_ocpy_close,		/* Class close callback         */
     NULL 		        /* Class close callback info    */
 }};
 
@@ -96,6 +113,9 @@ const H5P_libclass_t H5P_CLS_OCPY[1] = {{
 /* Local Variables */
 /*******************/
 
+/* Declare a free list to manage the H5O_copy_dtype_merge_list_t struct */
+H5FL_DEFINE(H5O_copy_dtype_merge_list_t);
+
 
 
 /*-------------------------------------------------------------------------
@@ -109,10 +129,12 @@ const H5P_libclass_t H5P_CLS_OCPY[1] = {{
  *              October 31, 2006
  *-------------------------------------------------------------------------
  */
-herr_t
+static herr_t
 H5P_ocpy_reg_prop(H5P_genclass_t *pclass)
 {
     unsigned ocpy_option = H5O_CPY_OPTION_DEF;  /* Default object copy flags */
+    H5O_copy_dtype_merge_list_t *merge_comm_dtype_list = H5O_CPY_MERGE_COMM_DT_LIST_DEF; /* Default merge committed dtype list */
+    H5O_mcdt_cb_info_t mcdt_cb = H5O_CPY_MCDT_SEARCH_CB_DEF; /* Default callback before searching the global list of committed datatypes at destination */
     herr_t ret_value = SUCCEED;         /* Return value */
 
     FUNC_ENTER_NOAPI(FAIL)
@@ -121,12 +143,222 @@ H5P_ocpy_reg_prop(H5P_genclass_t *pclass)
     if(H5P_register_real(pclass, H5O_CPY_OPTION_NAME, H5O_CPY_OPTION_SIZE, &ocpy_option, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
          HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
 
+    /* Register merge named dtype list property */
+    if(H5P_register_real(pclass, H5O_CPY_MERGE_COMM_DT_LIST_NAME, H5O_CPY_MERGE_COMM_DT_LIST_SIZE, &merge_comm_dtype_list, NULL, NULL, NULL, NULL, NULL, H5O_CPY_MERGE_COMM_DT_LIST_CMP, NULL) < 0)
+         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
+
+    /* Register property for callback when completing the search for a matching named datatype from the named dtype list */
+    if(H5P_register_real(pclass, H5O_CPY_MCDT_SEARCH_CB_NAME, H5O_CPY_MCDT_SEARCH_CB_SIZE, &mcdt_cb, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
+         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
+
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5P_ocpy_reg_prop() */
 
 
 /*-------------------------------------------------------------------------
+ * Function:       H5P_ocpy_copy
+ *
+ * Purpose:        Callback routine which is called whenever any object
+ *                 copy property list is copied.  This routine copies
+ *                 the properties from the old list to the new list.
+ *
+ * Return:         Success:        Non-negative
+ *                 Failure:        Negative
+ *
+ * Programmer:     Neil Fortner
+ *                 Friday, October 28, 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+/* ARGSUSED */
+static herr_t
+H5P_ocpy_copy(hid_t dst_plist_id, hid_t src_plist_id, void UNUSED *copy_data)
+{
+    H5O_copy_dtype_merge_list_t *src_dt_list, *dst_dt_list = NULL; /* Source & destination merge named datatype lists */
+    H5O_copy_dtype_merge_list_t *dst_dt_list_tail = NULL, *tmp_dt_list = NULL; /* temporary merge named datatype lists */
+    H5P_genplist_t *src_plist;                  /* Pointer to source property list */
+    H5P_genplist_t *dst_plist;                  /* Pointer to destination property list */
+    herr_t         ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    /* Verify property list IDs */
+    if(NULL == (dst_plist = (H5P_genplist_t *)H5I_object(dst_plist_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not an object copy property list")
+    if(NULL == (src_plist = (H5P_genplist_t *)H5I_object(src_plist_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not an object copy property list")
+
+    /* Get the merge committed dtype list property from the old property list */
+    if(H5P_get(src_plist, H5O_CPY_MERGE_COMM_DT_LIST_NAME, &src_dt_list) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get merge named dtype list")
+
+    /* Make copy of merge committed dtype list */
+    while(src_dt_list) {
+        /* Copy src_dt_list */
+        if(NULL == (tmp_dt_list = H5FL_CALLOC(H5O_copy_dtype_merge_list_t)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+        if(NULL == (tmp_dt_list->path = H5MM_strdup(src_dt_list->path)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+        /* Add copied node to dest dtype list */
+        if(dst_dt_list_tail) {
+            dst_dt_list_tail->next = tmp_dt_list;
+            dst_dt_list_tail = tmp_dt_list;
+        } /* end if */
+        else {
+            dst_dt_list = tmp_dt_list;
+            dst_dt_list_tail = tmp_dt_list;
+        } /* end else */
+        tmp_dt_list = NULL;
+
+        /* Advance src_dt_list pointer */
+        src_dt_list = src_dt_list->next;
+    } /* end while */
+
+    /* Set the merge named dtype list property for the destination property list
+     */
+    if(H5P_set(dst_plist, H5O_CPY_MERGE_COMM_DT_LIST_NAME, &dst_dt_list) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set merge committed dtype list")
+
+done:
+    if(ret_value < 0) {
+        dst_dt_list = H5P_free_merge_comm_dtype_list(dst_dt_list);
+        if(tmp_dt_list) {
+            tmp_dt_list->path = (char *)H5MM_xfree(tmp_dt_list->path);
+            tmp_dt_list = H5FL_FREE(H5O_copy_dtype_merge_list_t, tmp_dt_list);
+        } /* end if */
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5P_ocpy_copy() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:       H5P_ocpy_close
+ *
+ * Purpose:        Callback routine which is called whenever any object copy
+ *                 property list is closed.  This routine performs any generic
+ *                 cleanup needed on the properties the library put into the
+ *                 list.
+ *
+ * Return:         Success:        Non-negative
+ *                 Failure:        Negative
+ *
+ * Programmer:     Neil Fortner
+ *                 Friday, October 28, 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+/* ARGSUSED */
+static herr_t
+H5P_ocpy_close(hid_t ocpypl_id, void UNUSED *close_data)
+{
+    H5O_copy_dtype_merge_list_t *dt_list;       /* Merge named datatype list */
+    H5P_genplist_t *plist;                      /* Property list */
+    herr_t         ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    /* Check arguments */
+    if(NULL == (plist = (H5P_genplist_t *)H5I_object(ocpypl_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not an object copy property list")
+
+    /* Get the merge named dtype list property from the old property list */
+    if(H5P_get(plist, H5O_CPY_MERGE_COMM_DT_LIST_NAME, &dt_list) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get merge named dtype list")
+
+    /* Free the merge named dtype list */
+    dt_list = H5P_free_merge_comm_dtype_list(dt_list);
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5P_ocpy_close() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:       H5P_ocpy_merge_comm_dt_list_cmp
+ *
+ * Purpose:        Callback routine which is called whenever the merge
+ *                 named dtype property in the object copy property list
+ *                 is compared.
+ *
+ * Return:         positive if VALUE1 is greater than VALUE2, negative if
+ *                      VALUE2 is greater than VALUE1 and zero if VALUE1 and
+ *                      VALUE2 are equal.
+ *
+ * Programmer:     Neil Fortner
+ *                 Friday, October 28, 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+H5P_ocpy_merge_comm_dt_list_cmp(const void *_dt_list1, const void *_dt_list2,
+    size_t UNUSED size)
+{
+    const H5O_copy_dtype_merge_list_t *dt_list1 = *(H5O_copy_dtype_merge_list_t * const *)_dt_list1,     /* Create local aliases for values */
+        *dt_list2 = *(H5O_copy_dtype_merge_list_t * const *)_dt_list2;
+    herr_t ret_value = 0;       /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    /* Sanity check */
+    HDassert(_dt_list1);
+    HDassert(_dt_list2);
+    HDassert(size == sizeof(H5O_copy_dtype_merge_list_t *));
+
+    /* Walk through the lists, comparing each path.  For the lists to be the
+     * same, the paths must be in the same order. */
+    while(dt_list1 && dt_list2) {
+        /* Compare paths */
+        ret_value = HDstrcmp(dt_list1->path, dt_list2->path);
+        if(ret_value != 0) HGOTO_DONE(ret_value)
+
+        /* Advance to next node */
+        dt_list1 = dt_list1->next;
+        dt_list2 = dt_list2->next;
+    } /* end while */
+
+    /* Check if one list is longer than the other */
+    if(dt_list1) HGOTO_DONE(1)
+    if(dt_list2) HGOTO_DONE(-1)
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5P_ocpy_merge_comm_dt_list_cmp() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5P_free_merge_comm_dtype_list
+ *
+ * Purpose:     Frees the provided merge named dtype list
+ *
+ * Return:      NULL
+ *
+ * Programmer:  Neil Fortner
+ *              October 27, 2011
+ *-------------------------------------------------------------------------
+ */
+static H5O_copy_dtype_merge_list_t *
+H5P_free_merge_comm_dtype_list(H5O_copy_dtype_merge_list_t *dt_list)
+{
+    H5O_copy_dtype_merge_list_t *tmp_node;
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    /* Free the list */
+    while(dt_list) {
+        tmp_node = dt_list->next;
+        (void)H5MM_xfree(dt_list->path);
+        (void)H5FL_FREE(H5O_copy_dtype_merge_list_t, dt_list);
+        dt_list = tmp_node;
+    } /* end while */
+
+    FUNC_LEAVE_NOAPI(NULL);
+} /* H5P_free_merge_comm_dtype_list */
+
+
+/*-------------------------------------------------------------------------
  * Function:    H5Pset_copy_object
  *
  * Purpose:     Set properties when copying an object (group, dataset, and datatype)
@@ -207,3 +439,206 @@ done:
     FUNC_LEAVE_API(ret_value)
 } /* end H5Pget_copy_object() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Padd_merge_committed_dtype_path
+ *
+ * Purpose:     Adds path to the list of paths to search first in the
+ *              target file when merging committed datatypes during H5Ocopy
+ *              (i.e. when using the H5O_COPY_MERGE_COMMITTED_DTYPE_FLAG flag
+ *              as set by H5Pset_copy_object).  If the source named
+ *              dataype is not found in the list of paths created by this
+ *              function, the entire file will be searched.
+ *
+ * Usage:       H5Padd_merge_committed_dtype_path(plist_id, path)
+ *              hid_t plist_id;                 IN: Property list to copy object
+ *              const char *path;               IN: Path to add to list
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              October 27, 2011
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Padd_merge_committed_dtype_path(hid_t plist_id, const char *path)
+{
+    H5P_genplist_t *plist;      /* Property list pointer */
+    H5O_copy_dtype_merge_list_t *old_list; 	/* Merge committed dtype list currently present */
+    H5O_copy_dtype_merge_list_t *new_obj = NULL; /* New object to add to list */
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_API(FAIL)
+
+    /* Check parameters */
+    if(!path)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no path specified")
+
+    /* Get the plist structure */
+    if(NULL == (plist = H5P_object_verify(plist_id, H5P_OBJECT_COPY)))
+        HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
+
+    /* Get dtype list */
+    if(H5P_get(plist, H5O_CPY_MERGE_COMM_DT_LIST_NAME, &old_list) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get merge named dtype list")
+
+    /* Add the new path to the list */
+    if(NULL == (new_obj = H5FL_CALLOC(H5O_copy_dtype_merge_list_t)))
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+    if(NULL == (new_obj->path = H5MM_strdup(path)))
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+    new_obj->next = old_list;
+
+    /* Update the list stored in the property list */
+    if(H5P_set(plist, H5O_CPY_MERGE_COMM_DT_LIST_NAME, &new_obj) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set merge named dtype list")
+
+done:
+    if(ret_value < 0)
+        if(new_obj) {
+            new_obj->path = (char *)H5MM_xfree(new_obj->path);
+            new_obj = H5FL_FREE(H5O_copy_dtype_merge_list_t, new_obj);
+        } /* end if */
+
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Padd_merge_committed_dtype_path() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Pfree_merge_committed_dtype_paths
+ *
+ * Purpose:     Frees and clears the list of paths created by
+ *              H5Padd_merge_committed_dtype_path.  A new list may then be
+ *              created by calling H5Padd_merge_committed_dtype_path again.
+ *
+ * Usage:       H5Pfree_merge_committed_dtype_paths(plist_id)
+ *              hid_t plist_id;                 IN: Property list to copy object
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              October 27, 2011
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pfree_merge_committed_dtype_paths(hid_t plist_id)
+{
+    H5P_genplist_t *plist;      /* Property list pointer */
+    H5O_copy_dtype_merge_list_t *dt_list; /* Merge committed dtype list currently present */
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_API(FAIL)
+
+    /* Get the plist structure */
+    if(NULL == (plist = H5P_object_verify(plist_id, H5P_OBJECT_COPY)))
+        HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
+
+    /* Get dtype list */
+    if(H5P_get(plist, H5O_CPY_MERGE_COMM_DT_LIST_NAME, &dt_list) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get merge committed dtype list")
+
+    /* Free dtype list */
+    dt_list = H5P_free_merge_comm_dtype_list(dt_list);
+
+    /* Update the list stored in the property list (to NULL) */
+    if(H5P_set(plist, H5O_CPY_MERGE_COMM_DT_LIST_NAME, &dt_list) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set merge committed dtype list")
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pfree_merge_committed_dtype_paths() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Pset_mcdt_search_cb
+ *
+ * Purpose:     Set the callback function when a matching committed datatype is not found
+ *		from the list of paths stored in the object copy property list.
+ * 		H5Ocopy will invoke this callback before searching all committed datatypes
+ *		at destination.
+ *
+ * Usage:       H5Pset_mcdt_search_cb(plist_id, H5O_mcdt_search_cb_t func, void *op_data)
+ *              hid_t plist_id;                 IN: Property list to copy object
+ *              H5O_mcdt_search_cb_t func;      IN: The callback function
+ *              void *op_data;      		IN: The user data
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Vailin Choi; November 28, 2011
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pset_mcdt_search_cb(hid_t plist_id, H5O_mcdt_search_cb_t func, void *op_data)
+{
+    H5P_genplist_t *plist;      	/* Property list pointer */
+    H5O_mcdt_cb_info_t cb_info;		/* Callback info struct */
+    herr_t ret_value = SUCCEED; 	/* Return value */
+
+    FUNC_ENTER_API(FAIL)
+
+    /* Check if the callback function is NULL and the user data is non-NULL.
+     * This is almost certainly an error as the user data will not be used. */
+    if(!func && op_data)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "callback is NULL while user data is not")
+
+    /* Get the plist structure */
+    if(NULL == (plist = H5P_object_verify(plist_id, H5P_OBJECT_COPY)))
+        HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
+
+     /* Populate the callback info struct */
+    cb_info.func = func;
+    cb_info.user_data = op_data;
+
+    /* Set callback info */
+    if(H5P_set(plist, H5O_CPY_MCDT_SEARCH_CB_NAME, &cb_info) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set callback info")
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pset_mcdt_search_cb() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Pget_mcdt_search_cb
+ *
+ * Purpose:     Retrieves the callback function and user data from the specified 
+ *		object copy property list.
+ *
+ * Usage:       H5Pget_mcdt_search_cb(plist_id, H5O_mcdt_search_cb_t *func, void **op_data)
+ *              hid_t plist_id;                 IN: Property list to copy object
+ *		H5O_mcdt_search_cb_t *func;	OUT: The callback function
+ *		void **op_data;			OUT: The user data
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Vailin Choi; November 29, 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pget_mcdt_search_cb(hid_t plist_id, H5O_mcdt_search_cb_t *func, void **op_data)
+{
+    H5P_genplist_t *plist;      /* Property list pointer */
+    H5O_mcdt_cb_info_t cb_info;	/* Callback info struct */
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_API(FAIL)
+
+    /* Get the plist structure */
+    if(NULL == (plist = H5P_object_verify(plist_id, H5P_OBJECT_COPY)))
+        HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
+
+    /* Get callback info */
+    if(H5P_get(plist, H5O_CPY_MCDT_SEARCH_CB_NAME, &cb_info) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get callback info")
+    
+    if(func)
+	*func = cb_info.func;
+
+    if(op_data)
+	*op_data = cb_info.user_data;
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pget_mcdt_search_cb() */
+
diff --git a/src/H5Ppublic.h b/src/H5Ppublic.h
index 53818f1..e33b685 100644
--- a/src/H5Ppublic.h
+++ b/src/H5Ppublic.h
@@ -30,6 +30,7 @@
 #include "H5FDpublic.h"
 #include "H5Ipublic.h"
 #include "H5Lpublic.h"
+#include "H5Opublic.h"
 #include "H5MMpublic.h"
 #include "H5Tpublic.h"
 #include "H5Zpublic.h"
@@ -428,6 +429,10 @@ H5_DLL herr_t H5Pget_elink_cb(hid_t lapl_id, H5L_elink_traverse_t *func, void **
 /* Object copy property list (OCPYPL) routines */
 H5_DLL herr_t H5Pset_copy_object(hid_t plist_id, unsigned crt_intmd);
 H5_DLL herr_t H5Pget_copy_object(hid_t plist_id, unsigned *crt_intmd /*out*/);
+H5_DLL herr_t H5Padd_merge_committed_dtype_path(hid_t plist_id, const char *path);
+H5_DLL herr_t H5Pfree_merge_committed_dtype_paths(hid_t plist_id);
+H5_DLL herr_t H5Pset_mcdt_search_cb(hid_t plist_id, H5O_mcdt_search_cb_t func, void *op_data);
+H5_DLL herr_t H5Pget_mcdt_search_cb(hid_t plist_id, H5O_mcdt_search_cb_t *func, void **op_data);
 
 /* Symbols defined for compatibility with previous versions of the HDF5 API.
  *
diff --git a/src/H5SM.c b/src/H5SM.c
index 2fcaf7a..46e3140 100644
--- a/src/H5SM.c
+++ b/src/H5SM.c
@@ -1099,7 +1099,7 @@ H5SM_try_share(H5F_t *f, hid_t dxpl_id, H5O_t *open_oh, unsigned defer_flags,
     /* Set flags if this message was "written" without error and wasn't a
      * 'defer' attempt; it is now either fully shared or "shareable".
      */
-    if(mesg_flags && !(defer_flags & H5SM_DEFER)) {
+    if(mesg_flags) {
         if(((H5O_shared_t *)mesg)->type == H5O_SHARE_TYPE_HERE)
             *mesg_flags |= H5O_MSG_FLAG_SHAREABLE;
         else {
@@ -1109,7 +1109,8 @@ H5SM_try_share(H5F_t *f, hid_t dxpl_id, H5O_t *open_oh, unsigned defer_flags,
     } /* end if */
 
 done:
-    HDassert(!ret_value || ((H5O_shared_t *)mesg)->type == H5O_SHARE_TYPE_HERE
+    HDassert((ret_value != TRUE)
+            || ((H5O_shared_t *)mesg)->type == H5O_SHARE_TYPE_HERE
             || ((H5O_shared_t *)mesg)->type == H5O_SHARE_TYPE_SOHM);
 #ifndef NDEBUG
     /* If we previously deferred this operation, make sure the saved message